Now this is a line of commentary not often seen on Bimmerfest! I understand your point - these cars are so incredibly capable and so fast that driving them at normal speeds can be rather dull (in the case of the MR (I also have a 2007), it can actually be noisy and buzzy with VANOS noises at sedate speeds). I'd offer two suggestions, both of which have led to my keeping my MR for the long haul:
1) Find a nice twisty backroad and revel in the HANDLING rather than the sheer speed
2) Buy a vintage car, preferably a Bimmer or Porsche, and enjoy driving a slow car fast (ie, 40 MPH squealing around corners that a modern minivan would take with aplomb)
Of course, you could always throw in a roll bar and some five point harnesses and track the bloody thing - I guarantee that won't bore you in the least!
Good luck, mate!