No, desirability is the basis for value, all rarity does is affect price. When you go by value=rarity you fall into many ugly fallacies, (If you have tons of friends, is their friendship less valuable?) and fall by the speculators game. I like silver and gold, but more silver, platinum is an ugly ore, iphones are overrated. When I see a +3 weapon my only reaction is meh, it doesn't bring anything new or interesting and no ultra epic quest will make me want it more. If anything even less, magic items are to be enjoyed, the more you delay them, the less you use them and the less desirable they get.
(And I'd be thankful if in the future you avoided calling me a powergamer, what did I ever did to you? I'm not one, I don't enjoy that kind of play, I don't get it, and I suck at it. Just because I was raised on a more modern gamestyle doesn't make me a powergamer)