"...implementing diminishing returns when upvoting the same accounts (including own ones) again and again."
Were social interactions unimportant this would be practical, but the value of upvotes isn't only drawn by content quality. Society is based on relationships, and upvotes reflect social values other than content quality.
".. reintroducing the restriction to four (or less) full paid posts per day (from some hard forks ago) which was very reasonable."
How does this rein in socks? Actual conspiratorial malfeasance will route around such restrictions handily, IMHO.
Improved rep (UA, for example) is absolutely necessary. I expect that in time rep will be more important than stake, as the value of money decreases due to the paradigm shift in industry ongoing as individual ability to produce goods and services continues to decouple from capital.
The real power of social media rewards to change the world is due to that continuing deflation of economic factors, and the increasing import of other societal metrics.
Thanks!
I also have friends here on Steemit, and of course I am interacting with them and upvoting them. However, there isn't anybody I am upvoting ten times a day, there isn't even anybody I am upvoting five times a day. That's just not necessary to value their content (actually none of them is writing so many articles per day).
Nevertheless there are users who are upvoting own content (or the content of their sockpuppet accounts or their circle-voting friends) ten times per day. Only they would be impacted by a reasonable implementation of diminishing returns.
Folks I follow, @everittdmickey comes to mind, that do publish multiple posts per day, might receive multiple votes from me in one day. I often don't upvote all their posts (I do not autovote, and read most posts I upvote), but folks using autovoters might. @everittdmickey doesn't follow me, so this isn't an example of circle-jerking, just that I find good science and points in enough of his posts that I do upvote more than one a day sometimes.
Then maybe we just evaluate things somewhat different (that's no problem of course). I see no problem to upvote even best friends only two or three times per day, and spread ones remaining votes for example to some newbies who really need attention and motivation ... even with diminishing returns you still could upvote everybody as often as you like, it's just that every upvote would be significantly weaker than the previous one.