The idea of getting a dedicated race car is a better one than using a street car, no matter how well built, for race use.
Most people have no conception what the difference in driving is - they seem to think that if they have made loud noises and laid strips of rubber on the street they are somehow qualified to put on a helmet and race on a road circuit.
We had one guy come out in his super street prepared car and let him run around the track. He kept falling off the track. I took him out in his own car, didn't fall off the track, and posted 3 seconds a lap better times than his best 'didn't fall off that time' lap in only two laps. Also faded his 'racing' brakes to nothing.
I think Solo competition is great - teaches some technique with low risk to anything but cones, and weeds out the untrainable ones with much less risk to others and themselves.
Race track competition requires properly prepared cars AND drivers and I don't think I've ever seen a car that came off the street and did well on a track day. Ironically, they guys with the street cars that might possibly do alright on the track like modern Corvettes, Ferraris etc., are most likely to have owner/drivers whose judgements are hampered by over abundance of testosterone and they often end up screwing up far worse than the guys without chips on their shoulders.
PS - you are right - automatic transmissions are useless in road racing.
). The amount of work to fab and fit the full spec roll cage alone is significant. 
