AFAICS the Speaker's inventory is entirely pointless. I just save my motes for every second week when Xur has engrams. (early in the game, before I realised Xur had engrams for motes, I wasted a whole load on some pointless item from the Speaker thinking (I didn't know any better at the time) that a fancy Titan Mark or Warlock Bond or whatever was going to have some impact on gameplay. I just don't see the point in "dressing up" a character if it does not have some impact on attack or defence?)