I made my comment in May last year, and want to add something now.
Parts are expensive, BUT if you are handy with Google and a wrench then you can (A) get parts really cheap and (B) save buckets on labor cost. Sure, there are things that will cost you a pretty penny if they go wrong, but realistically what car today does not have these issues?
The 7-series is so far the most complex car I have owned, yet it's the most hassle free because I don't sweat the little things. If you look after the car it will look after you. Brakes, oil, plugs and filters can all be done yourself. Just keep the parts invoices
Would I get an E63/64 again? Definitely. It is going to be a classic, and bang-for-buck it is hard to beat at the current prices.