If you have a suggestion about the way the forum is structured, like where different forums and topics are, then raising them here means that site admins can implement them with the admin tool. It then is just a question whether the change is seen as a good thing. That's pretty easy.
If however you want to suggest some new idea or feature or functionality for the forum (we have quite a few of these), then you will get much better luck by searching the phpbb forum first (http://www.phpbb.com). The reason is that whereas the PlayDiplomacy code that handles all aspects of the game is all ours, and can be changed to do whatever we want, the code we use on this site for the Forum is the open source phpbb code. For non-techies, what this means is we are using something supplied by an internet community.
This codebase has many mods, additions, new features etc available in many different forms, so the reason it is worth searching phppbb.com is that the change you are interested in might have already been done. But if it hasn't, then it is not going to happen so there is no point raising a suggestion

By the way, if anyone is wondering WHY we do not change the phpbb code ourselves, it is because since phpbb is a supplied 'package' then when we upgrade to a new level we would then have to worry about reapplying any zaps to the code we have made, which makes it a nightmare and risks screwing up the forum for everyone. Best just to keep to 'official' phpbb releases and mods.
Up to now, when people suggest Forum changes, I have been googling phpbb to see if I can find anything that does what is being asked. And then I realized - why I am doing this? The raiser could just as easily do it - in fact, better to do it beause the raiser knows what they were after whereas I have to try to interpret from the sugggestion post what the raiser really wants.
So to reiterate. If you want to change the way the Forum works, include in your suggestions the reference to phpbb that tells us how to do it, and we can do it. Otherwise it is unikely anything will happen I am afraid...
I plan to sticky this post so that it remains as guidance.