A couple of additional thoughts on why Obama's address is unlikely to affect the healthcare debate:
1) The health care plans in circulation are already incredibly moderate. These are not single-payer, comprehensive national health insurance proposals, and yet the opposition has succeeding as painting them as a radical, slippery slope to government run healthcare. That strategy will continue even if the proposals become even more moderate by including the public option just as a trigger. No matter how Obama frames the proposals, the opposition will continue to insist he is just lying. There is no amount of effective communication when the opposition is this successful at generating mistrust.
2) Relatedly, oppositions don't care about specifics. Their job is to win electoral support by opposing. They will oppose for the sake of opposing, regardless of the content of the proposals or the President's framing of those contents.
3) Individual leaders and strategies don't matter.