You're always going to have a big whack of depreciation brand new, but there was a sweet spot of sorts to buy in where you got a basically new car experience from a purchase and ownership experience for quite a bit less, and you aren't in a hole for too long if you're financing either.
I have found the sweet spot I used to buy in (1-2 years old, plenty of plan, extendable to end of financing, if any) no longer exists for me. Either that or the cars all get snapped up too quickly since BMW had virtually no M8s they could show me and I'd have to 'downgrade a number' to buy new/er in the window. You have to go 4-5 years old and that (for me) reduces my appetite dramatically...
Your equation works for the E39 now is because the 'nicer' ones are into 7 figures (asking price). At some point when these were 200K and nice ones were 400, it didn't make any sense to do what you're doing. I feel like that won't happen for the E60 since you're 'restoring' an E39 that's neglected. An E60 in good condition will require that money on an ongoing (and sometimes unexpected) basis as though it is on life support. Either way, you have to play the long game. E39 will absolutely be worth keeping going if you have one, even at great cost.
Nothing wrong with any of these ending up as labours of love of course. That is the reality of what they are. I still love all of the above LOL.
Pretty much all of the 55s are great and unique experiences. The only major issue is the sensotronic brakes which have solutions nowadays and the ABC suspension issues on some (perhaps its only some years too) - which are also 'known' things that can be easily (and permanently) fixed nowadays.
