It is not PvP, so it doesn't matter how much money you spend on the game. Others won't be affected. They'll just say: "Wow, this guy is so cool and OP, I want this Warframe (or skin or whatever) too!" and that's all. And when you purchase something you still need to start from the beginning and master it (weapons, warframes), so it is somehow balanced.

Even newbies are completing other missions then more experienced players, so they'll meet only in some events or when the OP guys want to farm materials, or when it is your friend who is guiding you through the game.