It certainly does take a long time and a great deal of effort. We're lucky (UKBL™) in that I personally have a global 'reach' of some 300+ networks I can use for promotion and backlinks. Yet, I
still find it 'difficult' to promote! Ecademy is largely a lost cause as I think the vast majority of the users there have their heads in the sand. There's really only
one place to promote forums.
Other forums.
In answer to your question about traffic; they certainly do generate it but getting a forum going is the hardest part.
