Darvin: Attribute increases are some of the most valuable magic items you can get, provided the bonus is in the right place. A Sorcerer will kill for a charisma-boosting cloak, but a Fighter could really care less. Similarly, gauntlets of ogre strength are a must-have item for Fighters but merely a convenience (more carrying capacity) for Sorcerers.

Skill increasing items tend to be inexpensive, and can be particularly useful since you can swap out your equipment whenever you need them. They're good items to hang on to, but I wouldn't wear them as my default loadout and instead keep them as alternative gear for the odd situation where it comes up.