From what i've experienced the whole time that i've been playing Destiny is that one player runs into a big problem with upgrading legendary and exotic weapons/armor. This problem is mostly cause by how long it takes to build up enough Ascendant Energies and Ascendant Shards. You either have too much Energies and too little shards or too much shards and too little energies. This can be very aggravating and time consuming even if you spend a few hours completing the vault of glass along with nightfall, the daily and weekly heroic, you still might not have enough to upgrade a piece of weapon or armor. So pretty much you have to wait until next week to complete the weekly heroic and nightfall, or you have to rely on complete luck expecting for an enemy to drop a legendary armor just to take it apart and even then you only get 2 shards. What i would like to suggest is adding a vendor who will allow you to exchange one Ascendant shard for an Energy and vise versa. It'll be pretty efficient and would help balance out a lot of stuff. Of course you could tweak a few things in the idea but i dont see why this wouldn't be a good trading system.