I've owned my my 323i for over a year now. It was incredibly neglected and rough when I bought it. It has come a long way since then, and it's still a work in progress.
What I've done so far..
Bodywork: Two new front fenders, miscellaneous dents repaired, rear side signals deleted. Trunk por15'd and undercoated, floor pan patched por15'd and undercoated. $50 tremclad paint job.
Exterior: Euro bumpers, yellow highs, clear corners, all red tails, old window tint removed, new window lock strips, new badges.
Interior: New carpet (including parcel shelf), swapped near mint interior from my old 320i, reupholstered headliner, MPH speedo replaced with proper 220KPH speedo.
Mechanical: Cooling system overhaul including rad flush, new t-stat, fan clutch, water pump. Timing belt changed. Vacuum leaks fixed (I think). All new brake hardlines, stainless flex lines, rear calipers rebuilt, new handbrake cables. All new hard and soft fuel lines from the fuel distributor back, tanks removed, cleaned, por15'd and undercoated. New fuel filter. New plugs/wires/cap. H&R springs with new shocks. Diff rebuild with LSD internals from an e36 318is.
Future plans: New exhaust from manifolds back, new wheels/tires.