Again it's the racial profiling of insurance... people who heavily mod cars generally get into wierd accidents and like to try and commit fraud... you may not do it, but you are the exception unfortunately.
The GEICO rule for mods keeps changing... used to be that the first $1000 in mods was covered even if it wasn't underwritten on the policy (meaning you called and said hey I added $4500 in wheels/tires, system, and mods). IF you did call is it's covered, because we could take that into account and charge the right rate. Now I think it's technically covered to a point, but we just don't like highly modded cars. BTW GEICO won't insure me b/c i have Long Tube headers... that and they all know I track my car