My 1989 325is has 287K miles on her, and my 1984 318i reads 254K but the odometer works erratically so I'm guessing she probably passed 300K by now. Repairs ARE expensive, but they stayed fixed (so far) so I figure this is still cheaper than having a car payment. They are both beautiful and dependable. I would not hestitate to buy another high mileage car if it's been well cared for. Maintenence is very important. I do my own filters, oil changes, radiator flushes, etc. I even did my rear shocks myself. Very easy ... even for a girl (I'm female). But the front struts looked dangerous to attempt so I left that for a real mechanic. I expect to still be bragging about "my little girls" for many hundreds of miles into the future.
HOWEVER, I also have a 1980 320i (of course with high mileage but I can't remember what) that is a big financial headache. She had a bad life before I met her, which is probably why I've always had problems with her. So I want to say again that good maintenence is important for longevity. The concept works on people, too.