I'd prefer to keep the numbers the same, but change the rules so that a light truck/suv is only different from a car if it is used as a truck. Use as a truck means that that the value is based on mechanical condition and engine hours only. Cosmetic damage does not count, and an independent mechanical is needed to evaluate mechanical condition. This won't stop sales of Trucks/SUVs, but it will end leasing and renting - if you lease/rent a truck, fill it with boulders (which will put dents in the bed as they roll around) they cannot charge you damages, and on lease return are required to sell it for the same price as a truck that was used only for driving unloaded (or if discount it, the sales tax is as if it was in mint condition). Or drive it off road and dent the fenders sliding into trees and scratch the paint else where - no extra cost when you return it at the end of the lease/rental. Want to tow, that is normal for a truck so they can't say anything about you drilling holes for a hitch (so long as they don't affect the mechanical ability - if the truck comes with standard holes they can say don't drill, otherwise drilling is required and assumed okay)
Suddenly you could buy a truck as a truck, or a passenger car that looks like a truck. The truck will go for a lower price, but you will have to buy it (possibly under different credit terms as they less want to reposes it given you may do cosmetic damage). The car will be more expensive because they have to pay CAFE fines. Insurance on the truck will be cheaper: they won't fix hail damage, and if in an accident they will fix the lights but leave all the other dents. (if the other guys fault their insurance will not fix dents). People who actually need a truck for work purposes won't care, and they are also likely doing things that can't really be done in a more fuel efficient vehicle. People who just want a car will find cars a better option again.