[rpmerf]

Best:
Air / Fuel gauge. Upgrading to a wideband soon.
Lars 3.5 turn steering box
Clutch fan - I can actually feel a power difference
Relayed headlights. They are brighter than most 10 year old cars.
3 point seatbelts

Worst:
Can't really think of anything I've done that I didn't like / wasn't worth it in the end.
Body mounts - sucked to install and realign stuff
Dealing with rust