I tried to quit a couple of years ago. It lasted about 8 weeks. It was miserable. I decided to just take it one day/one race weekend/one track day at a time. That year, I raced when I wanted and when it was convenient. I did track days when they fit into my schedule. But I decided I wouldn't chase championships, because that, for me, seemed to suck the fun out of it.
I gotta agree on the formula 40 too. Fast guys, but no one's going to do anything stupid just to get the $5 piece of wood. The racing is close and fast. Most of them have been doing this a very long time.
I've come back to just riding for fun again. And it is fun again.
You'll know when you're ready to hang it up.