Again as I said thats a subset of the people getting rates, and sometimes thats not even how they got most of their rates. The bigger offender is the snowball effect that occurs in the games that reach the top of the top rated sort early on.
Also dont quite get what you mean by the last point as it could be two things. If its that the people replying dont actually play the games then thats why you make it so that they must play the game before you give feedback back with them giving feedback on the game page itself as being confirmation that they actually played it. If its that it buries everything else in the forums due to the constant activity then the solution isnt to stop it but to instead have a separate category. A thing a group does in the GMTK jam is has an organized rate swap where you get given 5 games every day from people who entered to rate and give feedback on. This helps remove that from the forums while still having it as an option for people to get noticed (with the 5 a day preventing abuse)