Well... the seller of those optics to you certainly didn't experience "hold their value and command almost retail prices used", but I understand your point. Say the OP had purchased an Aimpoint red dot for $600 instead of his Sightmark for $100-$150. The Aimpoint will sell for $450 used and the Sightmark is worth about nothing used. Either way, the cost of having the optic on the rifle would be about the same but one is a dimestore recreational optic and the other is top shelf duty worthy.