A friend of mine has a extremely nicely kept E39 740Li in Monaco Blue. The car has literally no expense left on its upkeeping. But my friend is a DIY, almost half a mechanic, so he does all work himself on his car. Saves a lot of costs and puts that money in other parts etc.
His daily driver is a GMC truck btw. So his BMW is only driven at weekends, but driven hard!
The Indy workshop who looks after my car is ex BMW, and works only on Bimmer group, so I regularly see Bimmers, Mini Coopers and Rolls coming in. The amount of money some guys are throwing amazes me sometimes, but these cars are money pits. Bottomless at that.
There is an American Captain who became a friend, who visits this place with his E53 X5 5.0 with a turbo and whatnot. The guy has a S500 in US as a daily, and only ever replaced some cooling hoses etc, whereas his X5 is always coming in for some maintainance.
So if you start counting money, its time to sell and move on, preferably to a new German.
Check out https://www.pakwheels.com/forums/members-member-rides/253660-my-bmw-e60 ride thread