For a collector, aftermarket porting hurts the value; in fact, it wipes out a substantial portion of the value, because serious collectors are all about originality. For a handgun hunter, it might increase the desirability. But, don't expect it to raise the price, necessarily. It's the old, old story of gun trading -- if I'm the seller, it's a treasure; if I'm the prospective buyer, it's trash. If I'm going to buy it we'll likely have to thrash out some middle ground between what you want and what I am going to offer, and it will end up being less than you're likely to get for an unaltered gun.