I bought Mida when Xur sold it once because I like scoutrifles. I upgraded it last week to new attack power. It still had 300 attack power. My advice is to just keep all exotic weapons. You never know what they are good for. I even saved a No Land Beyond :) Also save all gear which can give your health back for hard raids like Apotheosis Veil, Mask of the Third Man, Insurmountable Skullfort, Light Beyond Nemesis, Red Death, Suros Regime.