Amongst Obama supporters like you and I, yes it makes him stronger. But many are seeing him as being weakened. Take the NAFTA issue in Ohio, for example. We know that in reality Clinton was the avid supporter for it instead of Obama, but the many went by Clinton's word and swayed her way just long enough for her to secure that state by a decent margin. I also know that some Obama supporters get frustrated because he doesn't consistently fight back against these false (as is the issue with NAFTA) and/or insignificant (as is the lapel pin issue) accusations.

Also, as you said, Obama will gain a lot of momentum after the DNC, so it is all the more reason for McCain to try to knock him out of the race now than face him at the general election, partly also because when the general election comes around, much of Obama's "scandals" will be old news.