There are clear incentives for the community to have a window on what are the best-paid posts and the more Steem someone has, the greater their influence on the platform/pay.

Maybe. For those who are personally involved with dedicated curation of reward payouts, very likely yes. For major investors, maybe (depending on their own views on how important it is what particular payouts are made, some will care and some won't).

For many users, they may be happier looking at whatever Steemit thinks are the best posts to 'feature' or content that meshes with their own personal interests regardless of payout (possibly by app-level targeted curating, or just the user's own decisions of what to look at), or they may not even have a choice if their preferred UI (for whatever reasons) takes a different approach to showing content or doesn't even show 'content' at all (as with some of the games now reasonably popular on the blockchain).

I don't know how much demand there is for influencing the eyeballs of power curators, who are the only ones who can actually be counted on to have their eyeballs directed as a result of on-chain curation. There might be a bit more demand to influence the eyeballs of major investors (since that is a relatively valuable demographic to advertisers), but it still depends whether the investors care about payouts for their eyeballs to be focused on that content.

Saying 'curation' generally isn't specific enough, because Steemit does their own curation when they decide what posts to feature and what advertisements to place on the pages and where to place them. This curation exists alongside the curation of payouts and the former is more directly in line of users' eyeballs.

For users of UIs and apps that have their own policies on what content to feature, or none at all, those looking to reach those eyeballs will simply buy advertising from the app or UI operator, as with Facebook or non-blockchain games. Having a blockchain behind the UI doesn't change anything here.