Since you have the N52 you don’t really need to worry much on the reliability front, as has already been mentioned changing the salmon relays for the roof might help. If you have the auto box think about changing the oil.
Regarding making it more modern, LCI side indicators and LED bulbs for the angel eyes. Subtle styling mods and something I am currently considering, add a subtle boot spoiler, something I’ve already done carbon finer interior dash and door trims.
From there you can move to performance mods, as I’ve already indicated in your other thread, you can consider remapping the engine (forget what some might say about not to bother remapping an NA car) it will make it much nicer to drive since it alters the torque curve, not much additional outright power though but the difference is effective nonetheless, if you have an auto box remap that too with XHP Flashtool and add a throttle pedal box, I’ve done all those and all make a difference.
Suspension mods, M3 control arms upgrade for the front and some M3 components for the rear, helps with much better steering, also consider Bilstein B12 suspension kit or if you got more cash KW V3 or Ohlins coil overs.
Get more sound from that wonderful 6 cylinder with a sports exhaust. Speaking of sound, upgrade the audio system, better speakers amp subs etc.
I’ve done some of these and am considering the others.