I have an E39 as well as an E46.
One problem, I am a bit biased as my E39 has a bit more power than my E46. See my profile.
I can say that the E39 is a NICE car. They have their issues, but much nicer to drive on log trips and they hold a lot more than the E46.
Many of the same problems, headlight adjusters do break, you DO NOT need to cut open the later models to replace the adjusters, BUT it is not easy. Ask me how I know!
Rear door vapor barriers, dash pixels, seat adjuster cables, windshield trim are a few problem areas.
I would definitely go for a 530, slight tint on the windows, sort the headlights and polish the headlight lens, put a fuel pump in it, check the cooling system over well and sort the vacuum leaks, you will have a good car.