(Hey, first post btw!)
After realising that very expensive items that have spells with DC are only useful against low level NPCs, I have looked long and hard on how to make items with higher DC. I was very surprised to find that the ONLY way to do this is to use Heighten Magic during item creation to increase spell level (you can look it up, but this is a fact according to RAW).
A Hat of Disguise for example then increases in cost by 19800gp to increase the DC by 2 (slvl_2 * clvl_3 * 1800 = 21600).
For reference, DC is: 10 + slvl + minimum ability mod to cast spell.
I'd like magic items in the game to MEAN something, and to try to make them a bit more mythical. If they are a doddle to save against, they are pointless. On principle many items should be more powerful than the players to add to the mythical feeling.
I have already littered my game with house rules and I am comfortable making more, but I'd like some advice as to not break things that I wasn't thinking of in trying to fix this "issue". I have tried out multiple iterations of how to square bonuses and spell levels for a decent cost progression.
My plan:
First: In my setting, magic items with a spell DC will have a flat inherent +2 bonus to spell DC, so the formula for items is: 10 + 2 + slvl + min ability.
Second: At item creation it's possible to add up to +3 enhancement bonus to DC by increasing the gold cost of the item:
bonus * slvl * 1000
ALSO: At item creation, the maker can still use Heighten Magic to boost the DC "the normal way" (by increasing slvl and clvl).
OR: Forego enhancement bonus to DC and make it an intelligent item, with its own ability score, which is surprisingly cheap. Though but with a max slvl of 4 for non-dedicated spells.
My question is if I am missing something obvious here? Could I completely break some spell items with these 2 changes in ways I haven't anticipated?
Has anyone else been through making some homebrew change in relation to items with spell activation?