I finally did it! I loosened all 5 strings (again), gathered all my meddle and tried loosening the truss rod with more force force than I thought should be necessary. Suddenly I heard a muffled crack sound (the good kind) and the wrench started to move. I tightened the wrench some and what an incredible difference! My Ibanez bass is so much easier to play.
I can only guess the bass living first in bone dry California, then in a few hyper damp SE Asian countries modified the wood bit. Or maybe more than a bit.