They do require a LOT of maintenance but all of the issues have relatively simple fixes. The main things that can go wrong:
Leaking air springs. Upgraded aftermarket replacements with lifetime warranty = $1000 total for all 4 corners.
Torque converter leaking seal leading to failure. Upgraded aftermarket replacement = $1000.
The engine and turbos are perfect and will remain so with some care (and not trying to boost them to 20+ psi). Remove evil pre-cats from downpipes to keep heat away from block/turbos, replace old crappy hoses with new silicone replacements, remove crappy failure-prone aux water pump before it fails, add phenolic spacers to intake manifold to reduce intake temps, replace stupid viscous-coupled fan with electric one, replace obsolete ignition system with modern (and cheap) coils, etc. Total of all preventative engine maintenance maybe $1000.
So to keep the engine in better than new shape I'm at $6k. If the trans and suspension fail more like $8k to fix those for the lifetime of the car... worth it IMO.