the E38s were never,
ever meant to be cheap cars. the parts will never get cheaper. they (and other flagships) had technology in them that few/no other cars received until years later, which led to further issues. these are the cars the original owners dropped off at the dealership and came back with a blank check to pay for the service.
this is what happens when you buy a car that once sold for about 80 grand for less than a tenth of that, 10 years later, with over 100k
That is exactly what I was going to say. Further more, the reason why it is so cheap is due to the price to maintain them. That's why Benz's go for stupid cheap with high mileage. The price of parts are not going to change over 10 years, no matter what the resale.
On top of that, something that isn't rare is going to be hard to sell. Nobody is really looking for a run of the mill luxury car that is a decade or more old. It's really hard to get a fair price.
If it is rare, then you get into an accident, your car is done as it doesn't have good resale, but you can't find another one, especially for what your insurance will pay out. I have had a few friends with various 80's M3's, M5's, and one with an M6, as well as just very clean 3 series. Some have been totaled out due to poor blue book but were pretty valuable to the right buyer. They ended up getting screwed.
My advice would be to just figure out if you can afford it and go from there. If you can, have fun with it. If it's going to drain you, it may be in your best interest to sell now. For someone like me, right now, in this economy, that car would have to sit because I just couldn't afford it. I will admit that I can't do all the regular maintenance that isn't absolutely critical on my Honda right now. Believe it or not, it's usually easier to own a car when you are younger, after you make the initial purchase. You lack expenses, you usually can get a ride or even can borrow a car when yours breaks, parents may be willing to lend you a bit, etc.
Sorry, don't want to be a downer but I have a car with far more issues, is far less reliable, and is much more expensive to maintain than yours. It isn't my DD, or even a weekend car right now, but at one point it was. I love the car, plus it was a father/son thing so he paid a lot of it, even then it was a huge pain.