I see what you are saying, but if you already have the same exotic for all three characters, then yes, you should get another one. Also if you want the shards, you can always buy them from Xur for 7 strange coins. If you get all the exotics for ALL characters, then yeah you shouldn't get anymore. Honestly you probably wouldn't play the game anymore because you would've done everything and have completed the task pretty much everyone is trying to complete. Then there's pretty much no point in playing anymore.