530d isn't quite that wise. Massive injectors cost a fortune just to refurb. Numerous pumps and filter in the fuel system all play up with proper miles. Multi link suspension bushes are a bugger to diagnose. Hedgehogs fail. Head unit and dash displays loosing pixels... And of course, don't forget the essential swirl flap ectomy.
And if auto the box can't take a chip upgrade.
Sp apart from that...
So all in all just like most other cars then?

Personally it's the E60 530D LCi M Sport Model that i'm interested in so will only comment on that.
Swirl flap blanks are cheap and easy enough to fit (inlet easy to remove)
Dash displays loosing pixels isn't something i've heard of although LCD panels will be available in the same way as the Sharp LCD panels are available for CID's.
I know there can be issues with the iDrive controller that sits in the rear wing and can get soaked and destroyed by leaking sunroof drain tubes that have a design fault that stops debris flushing through (they are crimped so narrower and get blocked), easily fixed just like we know how to keep an eye on Omega Scuttles!
Suspension, can't really comment apart from the fact that every Omega (4 in total) i've owned has had to have new shocks, springs, wishbones, pollybushes, donuts, droplinks etc etc to get them to drive how they should.....
DPF removal is also a viable option and should release a few more ponies.