@Justin Wang: I can see that reworking some items would probably be a lot less work from your end ;)
I would note that in about half the games where I have +SP items, they're technically +Dex items. It's not uncommon for a Dex-based character to never find a single +SP item. Also there are games where getting 19 Dex is entirely reasonable. (If you get the gun and a Dex altar for example)
If you want to limit the SP cap characters reach more effectively, you could also have every odd Dex level grant +maxSP and every even Dex level grant +SPregen. That would also further differentiate SP from Mana.
Also as a player I prefer if +regen item have properties like +50% SP regen, rather than -1 turn SP cooldown. The scaling is different, with the former every next pip of SP regen has a smaller relative effect, whereas with the latter every next pip of regen is more important than the last. Which makes me feel like I have less options, because if I commit I have to really commit, and with the randomness of a roguelike sometimes you can't really commit.
@Random595: with mana-based builds it feels reasonable that you have to use mushrooms to get your mana back up in the late game. It doesn't quite feel the same with SP-based builds. Not sure why.