Once you've hit the level-cap for a season, Prime Engrams basically lose all of their value. Sure, you can hope for getting a God-Roll drop from one of them, but the whole purpose of Prime Engrams is that they're supposed to be useful for upping your Power-Level, and once you're at Max-Level, they just become a kind of an, "Oh, cool" feeling. Why not give us an option to sell our collected Prime Engrams to The Spider? From a Lore Perspective: Are we really supposed to believe that The Spider wouldn't have any interest in Guardian-Style Weapons of high-power? And the engram "Data-Compression" technology used to create them? From a game-mechanics perspective: It gives us a use for our Prime Engrams after that point where they start to feel useless and pointless. Give us an option to bring them to The Spider and trade them in for things: +50 Planetary Materials, +5 Enhancement Cores, +1 Ascendant Shard, +25,000 Glimmer, etc. We already have about 100 different kinds of currency in this game that we have to sort through just to manage a single upgrade to an armor piece. At the very least, trading in Prime Engrams for a choice of different materials would be a nice way of making that grind a little more fruitful.