I did some of both campaigns on Novice, but then went back and did them all on Skilled, then left it for a bit and did them all on Elite. The gradual progression that you make elsewhere in the game (online, racebox) makes it much easier when you step up the difficulty settings.

I have some sort of OCD when it comes to things like this anyway, I much prefer the feeling of gradual improvement than trying to nail something first time.