How things can change:

[bjack]

It's used car lingo.....the industry (car dealers) and the car pricing associations such as the Kelly Blue Book, National Automobile Dealers Association (NADA) and others will decrease the value of a car if its been modified beyond the manufacture’s specifications. The exception being high value classics, antiques and modified muscle cars of the late 50's, 60's and 70's. Of course this only works in one direction, when you are trading in the dealers will be quick to decrease your trade in value but will resale it for a greater profit (usually). Insurance companies also frown on mods, they only want to restore a damaged vehicle back to its original state unless you have specifically listed all modifications on your policy, and you will pay for this additional coverage.

Bottom line: When we modify our cars we enter a smaller field of potential resale customers. Only those of us who appreciate the mods and have the ability to secure financing or out-right purchase the car would be interested. This eliminates the larger field of potential customers who otherwise would not want to buy a modified car.
It’s really hit or miss, depending on how subtle the modifications are, I really don’t think dual exhaust would be a big deal in most cases. Too bad you lost that, but maybe you can find a good GT or if your lucky a Cobra!! You will pay more for insurance though.