I've forgotten the exact details, but once a stat reaches about 50, it has to get a lot higher before any stat it affects increases. As an example, there's a Relic suit of chain mail in MM6 (Apollo) that adds 20 to all resistances and luck, and drops your endurance by 30. A character with about 60—70 Endurance loses roughly 3 hit points by wearing it.There are exceptions, of course. For example Speed determines who goes first (among other things, I assume), and it can help if you can kill a monster before it gets to attack you. Also, you might want to get a stat well up to take advantage of the Challenge pedestals etc.
Resistances are different. Item that boost all resistances are greatly undervalued. On the other hand, unless you find them unusually early in the game, items "of the GODS!" are only good for resale, in my opinion.
