I think he's past the point where coming forward and being honest could help him. It's far, far too late for being 'honest and straightforward' with legal or quasi-legal tax evasion, or politically questionable investments, much less anything worse.
The only way releasing them would help him at this point is if, contrary to pretty much everyone's assumptions, the only reason he's refusing to release tax returns really is his privacy concerns. If he can come out and say, "Yes, I made a lot of money and I also gave a great deal to charity and paid my fair share of taxes" then releasing those records will help.
I suppose the one other scenario where releasing them would at least make sense is if the Romney campaign knows that those records are going to be leaked prior to the election, in which case the sooner they get whatever controversy they hold out in public the less damage it will do come November.
True, Bush probably would have had a real win if that DWI didn't come out 3 days before election day.
