I was faced that decision at then end of lease with an '02 M5. There was simply no better car on the market at the time. Plus I was 8000 over mileage and would have had a big penalty turning it in. The E60 was still several years away so I bought out the lease and kept the car for 2 more years until the crankcase ventilation issue at high mileage scared me away. I ended up trading for a 650i. I regretted that move and went for an '08 550i.

Bottom line, although an expensive way to pay off a car in the long run, buying the lease out makes sense if you like the car and see no advantage going for a new one. Plus you can work in a CPO process and get an extended warranty. You do that by selling the car to the dealer, then they buy out the lease, add the CPO, and sell it back to you, all in one transaction. To keep the M5, I signed sellers documents and buyers documents. Weird but it worked and only cost me $2000 for the CPO plus transaction fees (all added into the finance agreement).

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Richard
Sir Snaps-a-lot, 9 Time Dragon Slayer (54 runs!)
2011 X5 50i Alpine White, Biege Nappa /Lt Poplar M Sport
2009 Z4 35i, Black Sapphire/Ivory-Black/Anthracite

Gone but not forgotten: '08 550i, '06 X3, '06 650i, '02 M5, '99 540i