Oh god the races are so frustrating :(
I just went back to it, and the races on the overworld have pissed me off so much, particularly the flying ones.
It wouldn't be too bad if the characters/vehicles actually flew properly. If there was a proper turning arc that wouldn't take you a half hour to turn left, and if you could accurately increase/decrease your elevation, then maybe the races would be enjoyable. But sadly they're just frustrating.
I think I've gotten all the overworld races though, as well as all Help Stan missions. All quests are done too.
I've just got to get all the minikits from the last 8 missions, and then do the 2 last extra missions.
I'm at about 70~% complete.
I must say though, Lego Batman 2 is much easier to 100% than LMSH.
Lego Batman 2 was a lot easier to 100%. It makes my only 100% achievement game on Xbox.