RE: Are all RC forum's activity in decline?
I think every possible RC subject has already been discussed ad nauseam.
There is just not much left to talk about. In the early days I found RC Online / Universe tremendously helpful. I still love to build and fly, but I don't have much new to discuss online.
I perceive a similar decline in other forums that I visit... bikeforums.org, qrz.org, subaruforester.org. I suspect fourm participation is generally declining. People have become saturated.
And also, I do think the RC Aircraft hobby is declining in general. The generation that loved aviation is dying off. The younger generations do not have the same connection to flight.