I played a Daggerspell Shaper not too long ago, largely because 3.5 didn't really allow me to do what I wanted, so I took the closest fit, which was DS. Not broken, not underpowered, it's really just a way to allow druid/rogues to advance in wild shape and sneak attack and spellcasting at the same time. I hated the fluff, but my DM did his best to work it in, so I went along with it. The fluff isn't bad per se, it just had to be shoehorned in, and it felt like it. Anyway...
I would use the Pathfinder Chronicler save progression (good reflex and will, bad fort) - Pathfinder has done an excellent job of balancing prestige class saves so that they aren't ridiculous anymore. Keep the BAB as is, the spellcasting progression as is, the sneak attack progression as is, the dagger specials as is. The wild shape is a tough one, due to the changes. You could keep it as is with regards to the size restrictions, and make the 2nd level power the equivalent to Beast Shape II and the 4th level power equivalent to Beast Shape III. NO elemental or plant forms allowed. Change the skill prereqs to Knowledge(nature) 5 ranks and Spellcraft 5 ranks(there is no real analogous skill to Concentration, so maybe they need to master druidic spellcasting to use it in this new way?), keep the rest (or lose the alignment restriction, if you don't care for it). Class skills changed over as appropriate, I might lower the number to 4+Int, then again, I might not. This is a quick and dirty conversion, but it feels okay.
These guys lose Venom Immunity, Thousand Faces, and Timeless Body, as well as unlimited wild shapes (at 20th Druid), as well as having lower sneak attacks and no rogue talents or specials (as only 1 level of rogue is required). Animal companions are a bad idea, they would certainly be better off choosing the domain over the companion, as the companion will not get any better for them, and will become a liability or a nonentity. Seems balanced to me, once you throw in the loss of 2 spellcasting levels (minimum). Run with it, and have fun.
How would you handle the classes ability to keep magic enhancements from equipment, since they now get to anyway?
Didn't think about that. Well, I guess since they get that anyway, you might could do something to replace it, or not, since it's not that big a deal.
If you choose not to replace it, you will have a hole in the progression. This is okay, though it might annoy players. It is balanced, though.
Here are three other options.
1. +2 to Str and Dex while wildshaping, on top of the other bonuses. This is the easiest to track and use, and the one I like the least. It is balanced enough, all things considered.
2. Give them elemental body I and II, as a druid of 8th level. This is also fairly easy to track, and not at all overpowering. I feel that maybe they shouldn't get this, but at this point in their careers a druid of equivalent levels will have better wildshape, better spells, and likely equal or more skill points and hit points due to favored class, so it could work.
3. Give them a rogue talent. I like this one the best, it's flexible and not at all overpowering. I'd limit the selection to thematically appropriate talents, nothing too urban, and definitely NOT advanced talents.
Let me know what you think.
I like the idea of the rogue talent, and will probably throw one or two into the class.
One thing I was going to do was just have the prestige class stack with Druid for wildshape, but only allow it's enhanced claw ability to work with animals. Is that overpowered?
I wouldn't let it stack fully with Druid wildshape. The original prestige class didn't stack, and had a fairly restricted progression of its own. A prestige class is supposed to offer different options, not necessarily better ones. Don't step on the Druid's stuff. If you let HALF of the levels stack with wildshape that might be a good compromise.
If you allow half levels to stack. Remove any +times per day, or any other mention of wildshape from the progression (other than Fast Wild Shape, which should be kept). This leaves a hole in the progression at 4th, 5th, and 8th levels. Add some rogue talents to fill holes, and you've got something like the table below.
Level Special
1st +1 level druid wild shape
2nd Dagger claws
3rd Sneak Attack +1d6, +1 level WS
4th Rogue Talent
5th +1 level WS
6th Sneak Attack +2d6
7th Fast Wild Shape, +1 level WS
8th Rogue Talent
9th Sneak Attack +3d6, +1 level WS
10th Daggerspell flurry
This allows wildshaping to plant or elemental forms, unlike the original prestige, and it does allow huge animals and magical beasts, which is balanced under the new rules. In trade, they have fewer uses per day, it doesn't heal them like it used to, and they're not nearly as good as a Druid at it. A Druid 4/Rogue 1/ DS 10 will wildshape as though she were a Druid 9, cast as a Druid 13, sneak attack as a Rogue 7, with the rogue talents of a Rogue 4 at 15th level. Seems fair to me.
Upon reflecting, this is the version I would use in my games. YMMV, and bear in mind that in no way am I claiming to be some kind of design expert. Have fun.