cash out right now!
it would be hard to get a better offer, and by the time you find one, time will be lost.
I just came off leased '07 ('06 production) 335i 6MT coupe. At end of lease the buy out was $29 k, which I thought was a bit much. I ran that car up to 55k miles, that added up to hefty $ amount in mile overages. My initial plan was on buying the car out (thats why never worried about miles), and although this car never had a problem (except one solenoid replaced).... I knew all hell with car breaking down was about to break loose....
335i is a great car, best value for performance/handling/maintenance...but only for first 3 years, and after that... it is big trouble, too expensive to fix with out of pocket $$$...
Take the offer, ditch the car before something breaks and you'd have to fix it. Save up and get an M3V8 this summer