Note the following is 'scratching an itch', not preaching the one true way. A description, then the 'why'.
I'm changing the treasure in the armory of the Vault of Thorns as follows:
Replace ten +1 Orc Bane arrows with ten +1 Orc Bane (sling) bullets.
Replace one Orc Slaying arrow with one Orc Slaying bullet.
Modifying Gorum's Thorn as follows: Name is Mossy Thorn. Scythe instead of Greatsword. No user restriction (religion, race, class, alignment, etc.) Minor fluff changes.
So it reads as:
Mossy Thorn. The druids made a version of Gorum's Thorn that, while not the threat to orcs they desired, still served in defense of the marsh. Slot: none, CL 10th, Weight 10 lbs, Aura moderate transmutation.
This well-worn +1 keen scythe appears totally covered in moss except for the sharpened edge of the blade and the equally clean inscription on the blade. The inscription is in Druidic script, and translated reads, "A thorn in the foot shall cause even the mighty to stumble." When the wielder confirms a critical hit against any creature with the giant subtype, he can attempt to trip that target as a free action without provoking an attack of opportunity and ignoring any size restrictions related to the target. If the trip attempt fails by 10 or more, the wielder is not knocked prone.
So why? It scratches some peeves, mainly, and I don't think any of it is an overwhelming gain or loss in ability for my players.
First peeve is conceptual. I am frequently annoyed when some area that is dedicated to a pure race or class contains weapons or items that are unusable or antithetical to that class or race. Druids cannot use bows (normally). And while they might work with classes that can, I am not persuaded that in the heart of their citadel, meant for druids alone, they hold weapons to be used by others, but not them - not unless they had a significant surplus of weapons for themselves. The arrows become sling bullets.
Gorum's Thorn, a greatsword they cannot use, is explained by the base text. I could leave it, but then we run into a second peeve of mine, one found in many if not most adventure packs. It's a lottery device. It's potent and powerful but not game breaking, and only usable if one of your players happens to win the lottery - choosing the right religion (in this case), or profession or background or whatever. Some of it's acceptable or makes complete sense - holy symbols being one example. But this, which is the only Named Weapon of the module, and one of the only two such magic items of the module, feels a lot like bait and switch. In fact I believe this restriction is a good part of why the whole treasure of the druid council feels underwhelming -- look at this great toy, too bad you [probably] can't have it.
The biggest down check in my opinion was that it made the value of the weapon greater - it's worth about 17,700 GP without the restriction, or about 42% more valuable.
In exchange I get a weapon that's better flavored for its location when found. Its broader use makes it feel like a major award that balances the artifacts and major magic items earned in the other modules. Since the weapon won't be available outside the adventure and the original 'worked' in it, I don't have to worry about unbalancing effects.
So Silvermane, the Elven druid who was a member of the Council of Thorns, the one who SENDS you to the Vault of Thorns can use a longbow, but the fact there are magic arrows there seems inconsistent to you?
The only member of the Council you meet can use arrows... (Elves can use longbows; druids or not).
Gorum's Thorn is a +1 keen Greatsword. The trip on a crit is mostly neither here nor there. It's a keen greatsword. If you crit with it, the target is likely dead, tripped or not. At least at this stage of the game. Giants do not become frequent enemies until after Steelhand's Tomb.
And there is nothing which prevents Gorum's Thorn from being wielded by any party member. Indeed, the main fighter is certain to do so.
It is also a weapon that if offered to Karrguk as part of any deal will ensure that the Twisted Nail will betray Grenseldek.
Karrguk is a cleric of Gorum; it's expressly in the text. And Karrguk will betray the party, too, so the deal won't have to be made. Only promised and it makes complete sense to buy Karrguk's loyalty with such a promise - and Droja knows it.
I would also point out that Gorum's Thorn is intended to act as as blueprint for PC use (with modification of the deity involved) after they secure and reactivate the Forge in Minderhal and have the resources to craft their own weapons. So I think you are giving something early that is meant to be secured by the party later -- and as a reason to activate the forge (which others have complained appears to be irrational).
You might consider this and put it in the hopper.
Steelwind, I am rather bemused by your vehemence on what I admit are changes due to my opinion and taste, not recommendations for all. That noted, as you yourself said Silvermane has archery because elf, not because druid. I would expect Silvermane to have kept personal weaponry with him, not in general storage.
Re the thorn, I think the main fighter is using a hammer. In my particular group - which is, as I said, a major driver - the fighter is using the hammer and the paladin wont use it because Gorum. So I am left with a clogue, a spellslinger, and a druid.
As to the forge, the scythe, and a host of other items, make plenty of templates. Personally I think its greatest use is resizing the various magic treasure found throughout, but again that is my personal opinion.
There is no doubt that the primary purpose of the Forge in Minderhal is to resize weapons and armor. You are absolutely correct about that.
I do think, however, that while the Forge is aimed at providing the PCs a resource to resize weapons and armor (after they reach a level when one of them probably also knows teleport and so can make use of that resource as a matter of GM "hand waiving" later on in the AP), the Forge also speaks to the idea of the PCs using it to craft items, generally.
The lack of any central city tied to the adventure as a place to purchase and sell goods suggests that the PCs will be resorting to the craft magic weapons and armor and wondrous items feats more often in this AP than they will do in most of them (table variation of this tendency across groups of players is admittedly high I think).
Still, my point is that there is no lottery issue here with Gorum's Thorn. Its bonus ability to trip a giant on a crit is not accidental and it emerges usefully only in the later half of the AP through crafting, if at all.
The weapon is not evil, is not aligned and there is no reason why a paladin cannot use it per RAW -- and no good role-playing reason why they should avoid using it, either. Its additional benefit to followers of Gorum is there to deny that bonus to most PCs while making it useful for a role-playing purpose to bribe General Karrguk, who is multi-classed as a cleric of Gorum for just that reason, I think.
re the weapon, while the RAW allows, I disagree about the "no good role-playing reason." It's covered with iconography for a chaotic neutral god, and its bonus ability is triggered only for worshipers of that god. Admittedly this skirts the ancient arguments over whether a paladin can exist for gods who aren't one step from lawful good. Nonetheless I lean toward doubting the paladin would be comfortable with the implied association.
Of course, I'm looking forward to seeing how the paladin deals with not just iconography but an actual altar of an evil god that just happens to be oh so useful.
While there is a lack of a central city, the intro to the Forge mentions that the path the players take on this adventure brings them near the Sky Citadel of Janderhoff, Korvosa, Skelt, Glimmerhold, Braganza, Pangolais, and others. These make the necessity of returning to the forge for extended periods not so necessary. Useful, mind, but not necessary.
In the end, though, I don't think it matters. For my group of players, I think my relatively small changes will be met with enjoyment.
I cashed out Gorum's Thorn because that's what my players were going to do with it since they didn't win the character lottery, either. Instead, I used that amount of gold equivalent to drop in some homebrew ingots of enchanted metal that could be used to enhance MW weapons to +1 and two [insert subtype of choice]-Bane ingots so the party could customize their own weapons. I then added a small trade outpost that they could visit on the way to Fort Redlake so they could upgrade and refresh their kits.
Much better and more fun than some silly sword that was basically worth its presence in gold.