Having read through your post I think your stagnation was due to the wrong pitch, and, secondly and as odd as it sounds, due to that dorky faces illustration at the top of your landing page. I can't think of a single case where a forum maintainer would say "gosh, I need a better community building tool" rather than "I think I need a better forum". Then, say, he lands on your page and the first thing he sees is a bunch of ugly stylized mugshots, whereby what he's looking for is a single beautiful screenshot of a forum page... I mean it may sound like a minor, subjective thing, but the first impression lasts and I'm willing to bet that it had an extreme negative effect on your bounce rate. You got the "hello" completely wrong.
(I'm writing all this because I really liked what you've been doing and I still think it's a viable idea ... that you just happen to have overdone a bit).
We knew it too. But that wasn't the reason for our failure. Our sales pipeline was already quite full and so our focus wasn't on changing the pitch even though it was sub-optimal.
Instead we were trying to optimise the slow sales and onboarding processes as those were what held us back at that point.
It's the usual thing: We had limited resources, and so we prioritised based on what would achieve the most at the time. Even though our pitch was bad we didn't have a problem with populating our pipeline, we had a problem converting due to slow committee-based decision making and then onboarding an existing customised/bespoke forum.
Yes, our costs (even without wages) exceeded the revenue and would do so for a while. Revenue lagged behind the growth of costs, as is usual for affiliate revenue when the communities are being built rather than traffic being purchased.
The risk therefore was to the investors, whose support we needed to continue even though we hadn't secured more experienced angel or VC support (not a good signal).
(I'm writing all this because I really liked what you've been doing and I still think it's a viable idea ... that you just happen to have overdone a bit).