200 feels artificial. Over time the meaning of "200" has changed as the number of potential voters has increased.
However I would like to see your proposals combined. I think that there is value in adding to the current hall of fame say the best nodes of the last month and last year. And further it would be nice to be able to go back and look at the Hall of Fame at any given week in the past.
The value of that was brought home to me this Christmas when I first was busy and behind on PM, and then took over a week vacation. There is no way that I could reasonably skim the backlog, and I can't use "Best Nodes" to sample interesting conversations missed if I missed them by more than a week.
I think that the site has grown to a point where a more intelligent "browsable interesting history" is worthwhile.