Here's my thought on the subject. If the mods are choice mods, and have not been on the car for several years, yes they will help the cars value. How much will depend on what they are, and the perspective buyer.
The above statement about Nos, is somewhat true. Espesially these guys running a max shot.
The best mods you can put on the car to help resale are wheels, suspension, exhaust, and most of all the supercharger, twin turbo also, put plan on taking a huge loss with the twin tubo, as its cost is outragous to start with, but as I said it depends on how long these have been on the car, and will you as the owner of this car be able to convey to them, your driving habits, and care for the car. Believe it or not, many Viper owners do performance mods on there car, and do not beat on the car to much. They like the added power, but are very conservative with it. They never do clutch dumps, and non stop bumping on the rev limiter.
I've allways had good luck in selling my cars with mods on them, and I do loose some money, but not to much, as I don't keep the car very long.
A NOs car to me is the worst car to buy, not so much because of the NOs, but these cars are oftem owned by the most agressive drivers, but as I said that's not allways the case.
Skip White