Really this can only be done for people that have the internet on all the time, but its an idea none the less.
According to my stats ive only done around 3000 miles, but i have probably done the same offline (only been playing just over a month). I know its against AI and not real racers, but it would be nice if LFS logged your SP miles too, even of they were just stored on your PC and not put online, just as a general indication for yourself what mileage has been done.
Just a thought.