I've watched 'em. It would help your argument if you could at least pinpoint one or two things from the matches you cite...
Edit: Incidentally, why has this thread turned into a comparison between Federer and Agassi in their later years? I've lost track of how this pertains to the thread topic.
More power, better stamina, better reflexes. Basically everything anyone can do better when they're 25 than when they're 35 he did too.
Look at his returns for example, (In the 90's) he could hit winners from +200 km/h serves in surfaces that were a lot faster than the ones he played in the mid 2000's. In the AO 2005 he was aced like 60 times in a match (against Joachim Johansson). In Wimbledon 92' he made Ivanisevic's and Becker's serves look average at times.