Yup, 35+ is more than enough, but to be fair: Rallisport Challenge 2 had a lot of tracks, but many of them were just a smaller part of a larger track. I don't know if it's the same in Colin McRae games, but I wouldn't be surprised if that were the case as well in DIRT, given its amazing graphics.
As long as they're fun and not filled with straights, I wouldn't mind 35+ tracks.