Personally, I don't think you would have any issues selling a car with 70-75k miles on it, for the right money of course. There's an abundance of people out there looking for sub £20K CSL's and those that don't mind the 'higher' mileage ones. There a couple of guys on here with mileage in that region and I'm sure they'll be along soon to tell you what to look out for in these cars
Welcome to the Forum btw, I'm guessing by the Username you have an E30 M3 too? Photos to follow thank you!