I'd rather see all things purchasable with both vanguard AND crucible marks but at different rates. So for instance a vanguard weapon might be 150 vanguard marks, but 200 crucible marks (ignore the exact values). Vice versa for crucible stuff. It could be a .75 exchange rate, whatever really. Just give us more options. Commendations too, I would pay a glimmer tax to convert commendations, though I would rather commendations didn't exist at all.