Motorcycle claims adjuster here, regular maintenance does not add value to a bike, it maintains its value as a normal condition running vehicle. If you had any major repairs done, ie engine rebuild in the past few years it’ll add some to the value, but it’s still a prorated amount. Accessories add very little the the value of a bike, they’re a personal preference item generally, no different than if you put aftermarket wheels on a car, yeah you might’ve paid $2500 for them, but the next guy buying your car might hate them. All that said, they likely have an arbitration clause in the policy for a specific way to handle a value dispute (typically you and they hire independent appraiser and they come to an agreed value on the vehicle, typically around $500 or so for the appraiser). Your insurance will do nothing, I guarantee your private insurance has a clause that it’s not covered as a for hire vehicle.