I don't believe finance has actually got me any more sales (as people can get bank loans, credit cards etc) but I do enjoy the comms when I do sell on finance.
Don't think it will revolutionise your unit sales, it won't. Yes people ask all the time but often they can;t get it or will source elsewhere.
Comms on £3,000 car, probably around £250-300 depending on what deal you can get.