If the tower vendors were able to progressively upgrade any item to legendary similar to the way Xur upgrades exotics, this would solve many issues. Most importantly it would add re-playability and variety. I would be glad to delete a character and re-run it to L20 for some of those really nice looking early game weapons and armors, and end up not looking identical to every other guardian out there. This would also make use of materials and commendations, and keep the vendors relevant! It would essentially be a sort of convoluted extra-grindey transmog.