I've got a few mods but I try to use them sparingly. I only have modded LED saucers in RFM, for example. I have the video amplifier in it, but I don't consider that a mod either. I don't consider adding safety features like adding fuses to system 11 bridge rectifiers as a mod.
I also never charge extra for mods, I throw them in for free when I sell a game. I also save and throw in any original parts that were removed when I sell a game. If someone were to ask me to take money off for a mod, I would just tell them I'll remove the mod for free. Nobody has complained.