Made the switch in '01 and have no regrets.  Our planter and corn head needed replaced anyway and didn't want to invest more money into 36" equipment with no resale value.

I don't know if we improved our yields much or any with 36" rows but with 30" rows if we need to borrow a piece of equipment it's easy to find.  Having tires set for 60" centers isn't ideal but our bigger tractors have the duals on them pretty much year around and we have an older tractor which doesn't see field work with the rear wheels set out to 80" centers for mowing ditches.