its only an exploit if the exchange rates offer a net increase. If rates of exchange are the same in both directions there is no room for an exploit. Rather, what you would have would be players playing how they want and being able to exchange the rewards gleaned for the gear they want. That sounds like a great system to please the players. The only issue is making sure that the rates work together and do not favor one play-style an inordinate amount. The problem is bungie did not release a game that possess a well thought out method of exchange and player economy. Its all ad hoc changes because they messed up in the first place.