SOE needs gamers to spend money. PS2 isn't going to turn a profit just buy selling skins.
LoL and TF2 say otherwise. Although the majority of players won't buy any aesthetic item, a small minority will pay a ridiculous amount of money to make themselves stand out. See the skins in LoL or the hats in TF2 or the mounts in WoW.
As for paying for XP boosters, it's true that they do give you an advantage when you're new and competing against other new players. In the long-term, however, it doesn't really offer any advantage because everyone has already unlocked everything.