It is a brilliant motor and quite a relaxing drive, much easier to drive than the Z4 and fun in it's own way, but I can't face spending £1000 a month on maintenance anymore. That's assuming BMW can get you the parts you want, as you'll find many bits are no longer available and you need to scour the breakers - not that there are many to use for parts anyway - you might find the bit of trim you're after, but it'll be in black/grey/silver instead of champagne which then requires a retrim.
Every little bit seems to cost £250 from BMW - ignition leads, coil, starter motor, water pump, heater valve, pusher fan, radiator, etc. Then you've got the ever increasing price of the parts too - each year they seem to be 10% more expensive. Then the bigger bits cost £500 - alternator, MAF, compressor, etc.
It was off the road for 2 months waiting for parts and I was using a hire car, so thought I might as well by a car for less monthly outlay than the hire car - although over a longer period
Have tried the e39 and e60 versions of the M5 and while they are fast, they don't feel like M cars. The e39 just feels like a bigger engined 540i Sport, and the e60 takes you so far away from the road that it's like driving a simulation - you only know you're turning when the seat bolsters punch you in the ribs and you get no feedback from the steering at all.
I did consider an e46 M3 but thought they were too common for me - it's no good if there's more than 1,000 of them.