The value of any tokens is the community that is built around it. Adding the social layer on top of cryptocurrency is what was the killer app all along.
Suggested read: https://steemit.com/steem/@dan/steemit-s-evil-plan-for-cryptocurrency-world-domination
Also, Steemit is only the first app. Private blog will be built on top. Wikipedia replacement, scientific paper curation website and much more.
The network as no transaction fees too with 3 second transfer. How does that compete with bitcoin?
But how would you convince someone to buy Steem Power?
The first two are noble arguments, but in my experience people are not too keen on donating to content creators (eg. patreon, flattr, etc) or free services (eg. wikipedia, free software).
And although I'm no expert in finances, the third one just doesn't sound very convincing to me.
But most likely I'm already biased in formulating these points, so how would you describe the value proposition of investing in SP?