Pro tip
Just infuse your legendaries with the new higher rated blue weapons / armor. I've taken a 200 attack auto rifle up to 256 attack doing this, and will continue to do so when I get 280 / 290 attack blues as I progress up. Legendary weapons usually have far better perks and stat values than the blues.
This. And if you've got a legendary you definitely don't want to keep don't just dismantle it immediately. Put some motes/exp in to it to completely unlock it, but don't upgrade it. You'll then get 5 marks for the dismantle rather than 3.