Well gamification of the Steem Power is great, assuming it's not overdone. But the actual reason why anyone should power up firstly and foremost is for personal gain and I'm not talking about up voting yourself, I'm talking about seeing that 500 steem you bought at 0.25/1 grow to 1200 over a course of a year and start a power down when the price is 2.00/1, It's speculation for the most part, but a "game" some like to play, me included. I personally don't believe that I'll become a "superhero" here on Steemit in the next two years, but who knows, no one can predict the future,so neither can I.
Besides this there are many other reasons why would someone invest, I'm investing for the most part because I love Dan's vision on this, after much informing, reading, spending day/night here on Steemit consuming information like a black hole consumes light, I've accumulated so much information that I can really see the bigger picture, the picture that stretches far beyond Steemit and Steem as well, I don't wanna spread false information so take the following with a grain of salt, but this right here, could be something that would be a major historic part one day, if not as the one who succeeded, but the one who was the first one to attempt it.
TL;DR
Invest in Steem Power not for influence, but for possible personal gain.