Agassi wouldn't have much of a problem beating anyone in New York, including Roddick and Hewitt, except Federer.
However, let's remember that Federer and Andre played an epic two-day, five-setter last year that could have gone either way in the fifth set. Also, Federer will be going into Cincy without having played a match since Wimbledon. He'll undoubtedly be a little rusty and I don't expect him to make a run to the title.
As for New York, anything is possible. Last year Federer struggled in his first two matches against Albert Costa and Marcos Baghdatis. If his lack of match play and foot problems get the best of him then I can envision him going out early. If Federer is out then I think that makes AA, if not the favorite, then a major contender.
Finally, last year Andre had the misfortune of facing Federer in the QF's as the eigth seed. If Agassi stays where he is now, he won't have to worry about facing him before the semis or final. That might be enough to keep him relaxed and save his best stuff for a possible clash with the Fed Express.