I checked how Nadal has been doing after Grand Slams from 2005:
2005 AO, not in the later rounds
2005 FO, won, no rest and lost for Waske at Halle
2005 W, not in the later rounds
2005 US, third round
2006 AO, no plays
2006 FO, won, next week the first game on the grass against Fish who lost 7-6, 6-1, eventually Nadal retired against Hewitt, maby on purpose.
2006 W, longer rest
2006 US, longer rest
2007 AU, longer rest
I think Nadal has a potential letdown and Del Potro played a nice match ajainst ToJo but the Nadal is physically very strong and I do not believe he has started to party hardly, he is too professional and the most harm for Nadal on the grass, at least last year, were big servers. DP has a good serve and I have not seen him playing for a while but I think it has not developed yet as a killerserve. It was amazing last year how Nadal made the final at Wimbledon because topspin what Nadal has in his hits should be very unuseful but you can expect almost anything from Nadal, no play for me. Good luck if you will play this match.