We have found that the more boards you have, the less people will frequent them all, and therefore overall fewer posts. Just look at some forums that have TONS of different boards. What do you see? Dead forums and a lack of interaction.
The reason why TPR's forums thrive in a time where social media has devoured almost all other forums is because whatever it is we are doing, we are doing it right, and I'm not about to make changes now when we've had over 10 years of people being familiar with our forum.
Can you even imagine? "Hey everyone, thanks for browsing over the last ten years, but now we're gonna change everything and move stuff around! Your favorite threads may not be in the same place you're used to them being in! Have fun figuring that out! Good luck!"
We broke down parks in their own separate discussion threads and the index is a sticky on the main forum: http://www.themeparkreview.com/forum/viewtopic.php?f=2&t=63853
Beyond that, we don't plan on making any more changes.