If you are going to look at buying an older luxury/performance car then its highly advantageous to be able to do most of your own work (within reason of course) - these cars are old now and are going to require regular attention to keep in good nick and if you constantly need to take it in for repairs you are soon going to lose your enthusiasm.
I bought a 2001 M5 a few months back and I am over the moon with it. I have been slowly getting it into mint condition, new headlight lenses, fog light lenses, suspension components, wheel refurb ... I also bought a brand new center consul (titan line) special order from Germany but is nice to know that you can still get anything you want for the car (if you prepared to pay and wait). I also found than in many cases its cheaper to buy stuff on ebay and have it shipped to SA than to get it locally.
An M5 is not really ideal as a daily driver in the sense that tyres are expensive, as are brakes and servicing. A heavy foot and a powerful car is seldom a good combination for fuel economy as I can testify (I am getting around 19L/100 around town and about 13L/100 km on the open road)
The 540i is a little more practical but don't dismiss the 530d, 530i or the 525i either - drive them all and see what you like and can live with.
There was a stunning facelift imported 530i for sale recently on Gumtree for a paltry R60k