I insure with USAA and did not have to add additional coverage for aftermarket parts so long as the cumulative total does not exceed $5,000 in the event of a total loss. That's what they say at least. I've fortunately never had to test this theory.
If you've seen my "pothole death" thread though, you'll know I'm about to get my two trashed forgestar f14's and pilot supersports covered under a collision claim, so we'll see how that goes.
EDIT: Didn't read all the responses. Seems I'm not the only one.
///2007 335i Coupe Space Metal Gray///Sports///Premium///6AT///Piano Black Forgestar 18" F14 8.5" front 10" rear///JB3///Cooling Mist CMGS Methanol Kit///aFe DCI///Stett Chargepipe///Tial BOV///BSH Oil Catch Can