Might it be that there isn't enough, because there is no specific forum for it, rather than there is no specific forum, because there isn't enough talk about it?
What do you suggest there be as a home for people into the likes of the TurboGrafx16 or 3DO or Atari systems? Should those people flood the general game forum?
Same argument could be made for any obscure topic you could think of. Why does retro gaming deserve special treatment?
Using your logic, Why not give create an anime sub forum, an automobile sub forum, a home improvement sub forum, etc. Sure, you could say those topics don't get much discussion. But might it be that there isn't enough, because there is no specific forum for it, rather than there is no specific forum, because there Isnt enough talk about it?
Should retro gamers flood general gaming forum? Sure, why not? though I really doubt they'll be any "flood" with the few retro gamers on here. More likely we'll catch a "leak" of retro discussion if anything. Seriously, the fact that a topic cannot live without its own sub forum is a sign that not many want to talk about it.
Look at the poll. You've only received 18 yes votes, of which only a portion are actual members, and of an even smaller number are actual active users. I'd say st most you'd get 2-3 active users in such a sub forum.