Just an idea. Each race can have associated areas of influence: Hive: Cooldown speed buffs, recovery, r-o-f increases Cabal: ammo increases, ammo pick-up, impact etc. Instead of by-planet materials, we can get materials by enemy or location (such as a Fallen stronghold). And I wouldn't make them engrams, per say, unless they were pre-decripted and very rarely legendary. It can possibly go this way as well: A grip, rail, or magazine doesn't replace one ability, it replaces a set of three abilities. It means a bigger bang for your buck, but also a gamble if you want to replace that extended mag for three other options.