I did read in a Bungie update a few weeks back that they are suppose to be bringing upgrade material economies to the tower. So hopefully that means shards, energy, and materials. I love this game but spending pointless hours looking for spin metal really sucks. at least make the materials a lot easier to find and more common.

I agree I see the reason you would want xur to sell them because it's a limited time but why not have vendors sell them for marks. You can turn in 50 for 5 marks and 25 rep(?) What about buying them for like 20 marks per 100 materials (shards and energy not included). Obviously this also means you either take away the rep gain from turning them in our leave the 10 marks for 50 rep exploit I don't think it's enough rep to make it worth it so leaving it would be fine IMO. Just my proposal for buying materials.

Because xur is here for only a limited time.