Hmm interesting topic, and I know who he was talking to when he came up with this ;P
I have quit once, like I said before I was a sponsored racer when I was way too young and was way to good at that age. I started RC racing because it was fun, and was even more fun when I was whoppin up on people twice my age, but then if I didnt win, I wasnt old enough to take the responsibility on myself so I just blamed everything in the world except me. This among other things started to make it very un-fun and with age, and moving on to Go-Karts and Formula Ford, I quit racing altogether.
I still bought the new cars when they came out and still have a pretty good fleet, but never "got in to" it again, for one there arent enough tracks in Germany that race what I want to, and parts availability isnt the greatest, also there isnt the interest from my co-workers to race. However I am a crew chief on a fairly successful real Drag Race team and that has brought the "feelings back"
Recently I added a T-Maxx to my collection and $3000+ later I have found the fun and now am starting to consider racing again on my return to the states, already have the Team Nitro TC3 ready and waiting, and a Revo is next.
When will I quit again???
When it takes over my life again, or when I cant afford to eat :P (well eating is over rated!!)
As far as what I see as the "Top" for me when I own and race a competitive 1/5 scale F1 car, own an A-10 with Turbines, or even a Turbine powered boat
Till then I have a 04 Subaru WRX STi to sink money in to get into the 10s