Not entirely sure if they breed racers or not, I do speed events and they're certainly a good way of trying things out on the car, and as mentioned above frightening the missus.
for myself though having now done a few and a few speed events it doesn't make the thought of doing my first race meeting a daunting prospect just now one of preference for being responsible for my own mistakes, and budget, hence the maybe.
Perhaps their biggest help to the racers is that the circuits are now used more, got to help keep they a viable business concern?