I don't see any reason why you cannot remove the lettering, its very easy. Then, when it comes to trade in just reinstalled them, they are cheap on eBay and a easy install. I also agree with you about the lettering, I also have thought about removing the rear and replacing it with Land Rover, the Discovery lettering is a bit over done.
A far as the price, NO I don't think lettering has to do with a cheaper price.
2016 Discovery Sport Santorini Black Metallic, HSE Package, HUD and Park Assist Pack, Climate Control Pack, 18" Inch Black Design Pack, Audio Upgrade Pack, Driver Assist Plus Pack, Protection Pack