I personally don't see Federer winning that many slams or that many AMS and I certainly don't see Rafa winning 24 AMS events. The Nadal slam count is very tough to predict.
I'd say Federer wins 15 slams (I am doubtful about this) and I think Federer will win 6 more Master Series (conservative estimate, however I do not think he will win more than 8 or 9 more)
Nadal is quite tough, his irregularities on HC make him very tough to predict. However given his age and the fact that he has at least 2 or 3 "for sure" good years it would be safe to say that Nadal can win at least 7 more Master Series, if not more. Slams are another matter, I'd give him 3 more French Opens and I'd throw in an Austrlian open or two and I'd like to think that he'd manage to win wimbeldon one day.....
If forced to choose, takin everything into account, what would you say?