Im 21 and I sold my EK9 6 months ago and bought a 2004 E46 M3.
It has had its ups and downs. Servicing, petrol, parts, ANY MODIFICATION, AND TIRES TIRES TIRES cost an absolute fortune for the car so a big heads up on that. On the motorways I can get 30mpg-ish. In city centre im lucky if its double fiqures. The car itself is massively heavy as well (1700kgs). With only 340bhp it is still extremely quick considering, but if you are driving it hard (or constantly sideways in my case) the tires and especially the brakes take a pounding on the track ... BMW will take £1200 off you for pads and discs with a big smile on their face ... the standard brakes are not even 4pots which on a car that fast that heavy feels like suicide at times.
Further more, if you still have the thirst to modify, IT WILL COST YOU. An intake for my M3 was £1200, coilovers and £1600+ and for a turbo kit, your looking at £15000 for parts alone.
Positive things .... it is a very quick car. Not only quick, but comfortable, luxurious and amazing fun to drive. It really is a wonderful car and made what i thought would be a horrible transition away from my EK9 very pleasureable. It gets massive amounts of attention as soon as you modify it and the potential is huge (a horsepowerfreaks stage 2 M3 turbo will do 0-200mph in 30 secs roughly (see video at bottom)
Its about deciding what you want and what you can afford. I got the M3 because I wanted something more "grown up" and something "the burds love". Now I have a post on here about buying a new Ek9 for track use as I simply cannot afford to modify or run the m3 to track standard. I think you may find yourself as I do, on the hunt for something cheap to take on the track if you go down this road ........ hope this wasnt too long a post.
P.S See my m3 below, got it standard 6 months ago.