you should offer engine insurance separately for people that already have mods... probably over 60% of the people on here have at least one of those thing (a lot of people have full bolt-ons)... so i think you'd get a lot of business selling just an insurance package say if someone has macht schnell downpipes (pretty much identical to AR), a JB3 (similar to procede), an active autowerke intercooler (a much more known name than AMS), forge diverter valves, and the aFe DCI...
you'd get my business...
i also don't get how there is such a big premium on things like scoops, oil coolers, and a drop in filter... none of those things can possibly cause any problems at all.. and if any of them do, you can just take them out and take your car to the dealer and they'll fix it without a premium.. the main things you should put a premium on is the tune and maybe down pipes or intercoolers (because no one is really going to take those out for dealer visits)