You're not. You're paying to play it more efficiently. I could spend 30 minutes collecting 8 Pokemon (lets say that gives you 3000XP) or I could use that same

You're not. You're paying to play it more efficiently. I could spend 30 minutes collecting 8 Pokemon (lets say that gives you 3000XP) or I could use that same 30 minutes to collect 16 of them and double my XP on top of that (giving you 12,000XP). This lets me play the game faster. You aren't buying anything other than the ability to do more with less time.