You say "devaluate" like items in this game have some sort of bartering value. They don't. The only value you should be concerned with, seeing as Xûr is the only exotic "dealer," and he only [i]sells[/i] them, is the strength of your team, be it PVP or PVE. The more exotics exist, the more people buy from Xûr, the better your team will be. If Xûr ever sells Gjallarhorn again, imagine how easy strike bosses will be. Imagine how quickly your raid team can kill Atheon. Xûr is a blessing that most people dismiss as a short-cut that noobs use to git gud, when he's actually a convenient way to ensure that your dreaded strike grinding goes quickly and smoothly.