Year 2 owning mine (N62 - 4.4) and after the initial thrill of ownership wore off, and my frenzy to purchase all sorts of thing for it, my wallet has revived.
As far as maintenance is concerned and according costs, I can't say it's much more expensive than any of our other vehicles. That said, the time involved to do simple tasks in say a Toyota, will take double if not longer in the E53, but then again the driving enjoyment factor is double or more...
It's all a trade-off I suppose. Would I buy one again...probably yes, now that I'm a bit more comfortable working on it and have the appropriate tools. Do I still enjoy the vehicle - yes, very much. Does it still look good (in appearance & design) - most definitely.
When thinking of the alternatives in a similar price bracket to my purchase price, I'm very happy with the E53. It's a very comfortable vehicle, safe and generally reliable (it's never left me stranded). That said, I have one of the last production E53's with almost all options and it was a two owner vehicle with BMW service history when I purchased it 2 years ago. No regrets and no big ticket repairs (yet).

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08/06 build 4.4i Stirling Grey over black