I'm not a big fan, personally, of the Mini's. I don't think they feel fun
enough given their prices and reliability. I got to participate in a BMW event driving Mini's around a little, made-up track and came away a little disappointed. Perhaps I expected too much. Part of it was also because I disliked the interior (style and ergonomics).
EDIT EDIT: If I were trading an E46 M3.... needed back-seats AND wasn't going FCG again (which I probably would..... i.e. 2009+ 335i), I would rather get something like a new or late model Mustang. You ain't gonna miss the horsepower then....
Or an FR-S/BRZ if you favour more handling/agility over power and would only have to fit little kiddies in the back....