I do this as a Saturday job just for some extra penny's but I enjoy it but the only difference is I do it for one person.
The guy has 8 cars modern/classics 3 classic bikes and a helicopter. I'll do maybe 1 or 2 cars a day.
He has me do it because of my dedication to detail and extreme care and I only progressed onto the more expensive cars because he noticed this. Also it's all in door work in a hanger which is ideal for in the winter as it has central heating.
I only charge £8 an hour but all the products are supplied, hoovers, pressure washer and there's a washing machine for the cloths to be washed.
He has asked me if I wanted to do another day there as he has a boat which needs doing to (moored at the local docks).
Where I am going with this is that there doesn't happen to be a local millionaire near you? Get your foot in the door there and then expand. I think I could seriously start this full time for he obviously knows a lot of other millionaires that he could put me onto so if you got yourself into my situation you could make a decent living from it.
Where I am I could charge £15 an hour and he would have me but I am happy with what I get.
I don't want to do it full time as I need different types of work to keep me interested otherwise the work feels stagnated and I lose interest.
Also for mobile work the startup costs are not going to be cheap! £30K minimum for a fully kitted out van i'd say.
I would say you should look into it but do it as a side line until you find out what your market is. Don't give up your job yet!