I think that might have been good a month ago... if you know you have potential negative issues to manages, the smart thing is to neutralise them YOURSELF. Romney's now acting like he's being chased down and any sort of honesty would be branded a 'confession' and considering he's been so firm on not releasing anything, it just adds to the flip-flop list.
This is the CORE message though of his campaign and he would take a major risk at losing middle class voters. I actually think if he came forward (maybe a bit ago), it would eventually go away because voters tend to forget things. That being said, I'm sure he's also potentially weary of a 3rd party candidate from someone should the entire thing blow up.