As whatsitgoodfor pointed out, Master Dorje (or Master Wand, Master Staff, Master Drilbu, whatever) can be great. My Psion (with Master Dorje) bought up a ton of Dorjes with a couple charges each remaining (or, stopped using his existing ones once they got low), and uses them when creating items to meet power prerequisites. After all, if you're spending the entire day enchanting a sword you don't need a huge number of power points.
IMC we added a Prestige Class (which I've posted on these boards before) that allowed "salvaging" of charged items, either to recharge them, or pull the valuable and/or magical components out to be integrated into new items. That way, a fully depleted wand can still be used for something other than a backscratcher.
There was another factor. I had a player (Rogue) going shopping for wands, but he'd only want to buy ones with 10 or so charges remaining. After all, he wasn't going to cast Fireball 50 times, right? So, in the near term he'd still be just as dangerous, for far less money. In fact, he was more dangerous; 5 different wands with 10 charges each is more dangerous than one full wand.
So, combine these factors, and depleted items now had to have a monetary value. The formula we used was that one of these items has 50+(charges remaining) percent of its total value at any time. So, 17/50 charges remaining means 67% price. A wholly depleted wand would still be worth 50% just from the gems and "residual magic". After all, when you created the item its material cost was 50% of the market price, and those materials aren't destroyed in the usage, so why should its value be less?