I have State Farm with a Full Coverage policy and have already spoken to my agent about this exact situation. Receipts(unless mods were done to your car beforehand, then just pics and date) and pictures of the mods on the car(unless it's motor mods) are required to be covered at no additional cost. So my $5500 Miata with say $25k in mods would be fully covered no matter the situation(theft, accident, weather, etc).