In the game I'm DMing I allow ability-enhancing items that
a) effectively increase your casting abilities and
b) have different types of bonusses e.g. morale, competence or even luck
Just present me with a spell that grants an according ability bonus and I'll let you use it to create a "variant" ability buff item (within reason, so nothing racial or stuff like that here).
for example: you're an item creator and you just want that lil extra strenght while already wearing a belt of giant strenght (+4).
if you've got "elation" (from BoED) on your list, I'll let you make an item that grants you a morale bonus to STR (because that is what "elation" does).
Slot restrictions still apply, though, so unless you go for a second torso you'll have a tough time wearing a belt of moralistic strength (+4) in addition to the regular one. of, course, you can have a slotless item but that IS gonna cost you some.
main effect is, these items stack with the PHB buffs. not much of a big deal, because my NPCs can pack that stuff, too.
standart item creators in my campaign don't do the trick on a regular basis, though, so these items a sold at 150% of the base item, if they're available at all.
Mal-"h"-a-"vo"-kh
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load your dice and brace your pencils cos it's numba-whackin' time
...and if any of you suggests I take less of that stuff you think I'm zoning out from then please be asured that I'm actually not doing so...