First of all, your money is as good as anybody's. Second, those so called fast guys will get over it. Remember someone had to look out for them at one point, they didn't come out of the womb roll'n fast like a pro. I still ride behind my son from time to time for protection from the occasional idiot. He's just turned 11, rides an 85, and he rolls pretty good. He went to Loretta's last year on a 65 in the 7-9 class, but there are still some jumps he won't do. For added protection on certain tracks I will follow him around when the traffic is heavy. I don't need one of those "practice pro's" scrubbing a big triple (or whatever) crossing 3 lines and trying to land where my son happens to be.
In all seriousness, it's sounds to me like you have it covered. Certainly based on his experience would dictate when you get on the track. If he has good experience on a track with big bikes and can hold his line under pressure, then I say go follow him when ever you want. If he still has trouble holding his line, I would only take him out on the track when the traffic is lite.