If a candidate went to a debate and started spewing policy specifics, they would come off as being wonky and boring. For better or worse- in my opinion largely for the worse- the presidential debates aren't about the issues as much as they're about political points.
But if you really want specifics they're easy to find. Both candidates have websites, and Obama's has hundreds of pages of policy proposals waiting for you.
Anyone who claims that Obama hasn't come up with specifics is just parroting Fox News talking points and is either too lazy or too computer illeterate to do the research and find the answers for themselves.
As for Nader, I voted for him twice. But if I actually thought he'd have a chance to win, I would have run the other way. For all the good he'd done the country in the past, his presidency would be a disaster of GW Bush proportions. Furthermore, Nader's campaign has become a grand gesture if narcissism . If it was really about political change, he wouldn't be running again himself, but would have put his support into helping to build the green party and break the two-party system we have now.