There's not a lot of market for them. You hardly ever see someone selling or buying just the empty frame, so you can price it at whatever you want. You'll get what someone is willing to pay. But generally a regular milling service, like an anodizing job, doesn't translate to more value on resale. It's like putting a new roof on a house... potential buyers expect the house to have a good roof in order to sell, so if you re-roof a house before putting it on the market you're not going to recoup that cost. It might help you get a buyer quicker though.