I cannot disagree about concentration of upvote power in the US. One thing I would say is even if Steemit decided to bring back the 24 hour period for rewards, it still would not solve the issue of where the article is placed in the stream. Higher reputation holders would still force lower rep holders down the list and time zone issues would still persist.
I think that curation and featuring content from others which speaks to you is something we need from everyone in the Steemit community, regardless of reputation scores. For purposes of this conversation, if someone in my feed started to feature content in their blogs, I would look to see if that content interested me. For my part, between my "day job" and writing, I could not possibly filter through all the content each day to upvote quality. It's something which needs to be crowd sourced and I think everyone has to do at least some of this to create the ecosystem we want. I think this could be a great work around to build dolphins in other time zones. I am not a whale or dolphin by any stretch, but if my curation and featuring posts happen to attract the attention of a whale, and by virtue of that give another in a different time zone, the attention of a whale, then the community as a whole benefits and so do I.
This post and our conversation has both made me realize where I fall short doing my part and inspired me to do a regular feature about the gems I find.