Spacers are definitely required, the wheels look a bit lost in the arches, what size, offset, tyres are you running? The skirts and spats accentuate it if anything. With the wheels further out it will transform it. Maybe a trust splitter or the later, deeper type would be nice, it'd be more in line with the rest of the kit. You would lose a bit of clearance at the front though.
Lose the rear fog light, it's easy to integrate into the standard rear lights, did a bit of a write up on how I did mine, it's a small cheap job. Could do with changing the front and side indicators to clear. You can convert the original nissan clear front indicators to proper clear for alot less than the aftermarket 1s, drop me a line and I'll give you some pointers on how I did mine. Ride height looks quite low, I like them low, buts it's just whether you can live with it.
Hope I haven't come across as too negative, just think a few small, not too expensive changes will transform it.
How many types of rear R34 GTR diffusers are there?
Also what the he'll do they look like off of the car as well as on the car?
I saw a pic of an ARC one some where...looked awsome but have no idea where I sAw that pic :-/....