"seeing value in it subjectively, is what is supposed to keep it afloat"

I think they need a more concrete reason than that. I agree of course that value is subjective. I mean, look at Dogecoin. I think it was started as a joke. But it's still going because people just think it's funny. Humans will value things for an unlimited number of reasons.

For steem though people are treating it as a potential social media game changer. We should be able to identify reasons that people value the currency.

I do think a major part of that is speculation/investment. People are expecting the market cap to increase.

Another part is the utility you get out of using the platform because it's so unique.

"investments are not inherently required"

Not inherently no but I think that's what got the ball rolling. Someone had to start trading bitcoin or whatever for steem in order to give it a price. I think a lot of that was from speculators. So if their future expectations are not met in the form of an increased market cap they might bail.

People also put money into the currency because of the utility it allows in using the platform. As I argued above for various reasons I don't think this will be sufficient to sustain payouts.