Rear diffuser would be awesome.
As far as bang for your buck, i would do a pillar gauge pod. NO ONE makes one that fits.
I would like to see
-Dash (maybe with 1 more gauge in the center?)
-Center Console
-Doors. not just skins, lets ditch our rust depositories while we are at it
-1 piece fender/headlight buckets
-Side skirts like below. (well i will have to upload that later, i dont have the pic on this computer) but it is a rust color z with black wheels and has a very clean sideskirt on it that goes on the door, fender and rear quarter.