This is just my two cents, and I am sure you will get lots of information over the next few days over this one. Modified guns, for the most part are an attempt to upgrade your average Joe gun, just like upgrading a car with fancy wheels and a booming radio system. Some things that you modify will increase its value while others will decrease. My feelings are if I were to modify a gun, say spending a hundred bucks just to change the trigger pull, its because I am getting it to keep it and maybe pass it along to my son later in life. I am not planning on spending that kind of money to tweak something that I plan on dropping off in the market unless something emergency like happens, for instance I lose my job or get injured and thats the only way I can pay my bills. I am going to be bold and say that the value of your newer gun will drop in value to some degree, if for no other reason, than the fact that once you buy it, and shoot it just once, its now used and why would another person give you, all your money back for a used gun when they can get an exact copy in actual new condition, for the same price. I would expect 10 to 35% drop, depending on the gun, if or until it reaches collectible status, or is a hard to find model. Even the hard to find models sometimes are not a favored of the public, so some people wind up stuck with it. Just my thoughts.