Unless you're wanting to fit a rear diffuser (as these are few and far between for bug eyes) and the clear tail lights, there is no reason to change it over..

IMHO, the 03+ bumper doesn't look as aggressive as a bug eye bumper.. the 03+ one rounds off more on the lower edges.. as a result, it looks "narrower".





Again, if you want to fit the later tail lights and a rear diffuser, go for it.. as its hard to find diffusers for bug eyes.

Otherwise, a set of spats will sort out the look pretty nicely