I think if you had to have a max level weapon to turn it in for the upgrade I would be less irritated.
As it is now, you can just turn in any weapon for the upgraded version, whether it is all the way unlocked or 1/2 way or not at all.
So all the guns that I've been putting alot of time into upgrading, mida multitool, last word, truth, thorn, etc, can be traded in without me ever having to touch them for a whole 7 coins.
I'm sure I'm bitchin for no reason, but seems shady to me. If Bungie would have said, hey maybe don't waste your fucking time and materials, telemetrys and hundreds of bounties, I wouldn't have a problem.
Tl:Dr - if xur would only accept max level Exotics I'd be happy. Time spent upgrading would have ment something.