I think the biggest culprits for weight on your car are two things you cant do without.. AWD and two Turbo's.
Bimmers are heavy, right in the sheet metal. I'll agree with the above comments about picking up a dedicated racer and keeping your car a pimpin street machine.
But if you do go ahead and do it... I'll be perfectly willing to make you an offer on your sports seats as part of my ZSP retrofit project.
Happiness IS the corner!