Im just not convinced about the desirability of an M3 Conv.. Regardless of the mileage! Its arguably the ugly sister of the E46 range.. It handles the worst, it is the slowest.. It has the chav image (rightly or wrongly), It's also hardly a rare car, If it was an ultra low mileage CS then I could understand it, If you seriously got offered £4 or £5k more than you paid for it then I think you are a little bit crazy to of refused., as that would of been another £5k towards a proper drivers car like a CSL
Seriously if you're happy with it thats all that really matters.