My issue with the EIP (and the whole concept of rewarding content just for the sake of it) is that even if it works out perfectly - i.e. the highest quality posts always end up with the most rewards or however you define the perfect "proof of brain" system - I still don't see how there is value to owning STEEM or why I would want to buy any

I'm not going to entirely disagree as I've been making this exact same argument since 2016 as many are well aware, especially regulars on the old steemit.chat #price channel.

However, I do want to make a counterargument which is that EIP and better voting generally may allow stakeholders to coordinate to pay out not necessarily the 'highest quality' content (which is a poorly defined concept in any case) but on content which brings value to Steem. This can happen in many different ways including:

1. Being externally popular (the best example of this I can easily recall is Dan's early post "Will the DAO be DOA" which was covered in popular media when The DAO was in the new first during its enormous fundraise and then during its hack. The steemit.com post was widely linked and discussed and probably helped give Steem a big early boost in attention and growth)
2. Being part of a process that evidences virtuous cycle growth, for example, externally-successful influencers with an audience being successful on Steem and inspiring more to join in turn
3. Contributing directly to growth by attracting users, but this only works if churn is also under control. This probably requires there being enough other "stuff" of interest on the platform/ecosystem beyond just free money, which most new users won't get much of anyway.
4. Supporting organic Steem influencers who develop their brand and attract a new audience to Steem.

There are probably others.

I don't know whether EIP will actually do this and if so I doubt it will do it right away, but it is possible that a stronger voting system will eventually allow more of the reward pool to be directed to these sorts of specifically value-adding content and not just content for its own sake or even just 'quality' content.