I think it MAY work both ways, I believe more activity can make prices go higher and if prices go higher, more people gets to know about Steemit and they get more excited about participating.

I do know for sure that at least the price as an influence in the activity on Steemit, for example: 2 months ago when I posted my Introduction https://steemit.com/introduceyourself/@mariacherries/this-is-me-introducing-me, there were a lot less people posting because there was a much smaller reward pool, in that post I got 133 upvotes but only 0.32 in revenue, and now that the Steem price is higher more people are more excited about posting.

The price hype is a little big trickier because that can be influenced by other stuff like China validating Steem and market cap