You should probably just do the best PVE part of the game, the raid, and not worry about the vendors selling gear for crucible marks. I've had my eye on an arc HMG from Dead Orbit, since I have yet to get the Thunderlord, but other than that I have no interest in any vendor item. Thanks to the raid and random drops I have almost 2 sets of gear better than vendor gear (raid sets) and I have a full solar and void complement of weapons. I'm only lacking an arc heavy weapon.