I was in the same boat the other day as you. My iPhone 4 still has the original 1.59 baseband. I only had it because it would be unlock able whenever via ultra snow.
Come to find out since I bought my iPhone on release day AT&T will unlock it on June 24th. I've already done this with an off contract iPhone 4 and the process is a piece of cake.
So really there was no reason to keep 1.59 anymore as come June 24th it will be perma unlocked via apple/AT&T forever.