Aye, it's not my favorite but it's a neat addition.
I'm finding a lot of challenges that ask you to go point-to-point in a certain time, and apparently expect you to take their ridiculous winding halfpipe to the sky to do it? I usually try to cruise past that shit and just finish it

I was getting annoyed with how little influence I was getting for challenges (200-400), but someone on /r/Forza mentioned that it's based on how popular it is. If you sort by new in the challenge browser, you can get 5200 influence per. Some of its a crapshoot but usually quite doable still.