GW2 needs a tweak...
Mounts are in the game already.
You don’t need to purchase Transmutation Stones as they’re already available by completing maps (which you should be doing if you’re PvE, anyways). If you’re plopping the skin onto a level 80 gear, you should be sure of your build beforehand, anyways, so there’s no point in buying Transmutation Crystals unless you’ve been Stoning your armor (but that’s a personal choice, just like wearing Cultural armor while leveling is a personal choice). Lastly, how would making people not spend money make Arenanet money?
Implementing a combat system like TERA’s would not make people spend money on the game.
And, to reiterate:
Mounts are already in the game, you can purchase them in the gem store.