i've built alot of these, and you're right. The paint job is what makes the difference. The only thing I add in my builds are panel lines alon the hull, and a few styrene strips here and there. If you're building red five, go nut with detail.. That's Luke's car, man..
But if you're making your own little baby, sky's the limit. a waring for the interior. When adding that scope on the long par tof the "dash" don't use and thing under it, as the canopy comes down real close. A targeting computer isn;t hard either, as are the hose lines. If you pick up one of those Tamiya soldier gear detail kits(1/35, for tanks too), it'll help alot.. and it's in spirit of the orignal. Good luck. B)
The most recent one I did was of the ROTJ Red 3 (with a Biggs pilot/R2). Some of the areas I worked on were panel lines and small details all over the hull, some small things in the cockpit like the targeting computer and random other little stuff, the rear deck behind R2, the detail squares on the sides of the hull beneath R2, the engine intakes and tops, the engines themselves, and also the entire interior of each wing was completely rebuilt. Here's a good shot that shows it: http://www.starwarsmodels.com/images/models/xwingps013.jpg I also added a bunch of lights just for fun. 
