Yes, return it to stock.

 

IMO - If you're going to trade-in to a dealer, return it to stock. Otherwise, leave it as is.

 

Believe it or not a modded car will depreciate the value of your trade-in. Some months ago I did appraisals in different places, and they all told me the same thing about my Evo. Take it back to stock and you'll get more money, and then you can sell your aftermarket parts and make even more money.