Great guide, it deserves a sticky for sure. I'm surprised nobody else posted this sooner.
AFAIK, a lot of these have been common knowledge for a very long time in organized races (CW's, GTT, WCL, etc.) I wouldnt know if its the case anymore though, since I havent actually played MKW in almost a year now.
I'd have to say that trapping
properly should be considered pro. Trapping normally and hitting, say people in WW's with traps is one thing, but consistently hitting other competitive racers with them requires more than knowledge of common spots. I'd say to be truly effective, trapping requires timing (which lap to lay traps and where, all the while not letting yourself get double/triple-redded) and the ability to quickly adapt/notice players' racing lines/habits.
This comment is very likely more than a year old though, so up to you if you want to consider it.

Last I was into CW's, the metagame shifted to Team Shocking, which shifted emphasis from proper item usage to activating stars/bills/megashrooms at the right time (vent ne1??).