Mark
I agree with your observation that there are a lot of topics that don't come up very often but sure seem to fit. I recall coming across forums dedicated to "tin boats" and thinking I wish they'd migrate here because the restorations and mods they were making were right inline with the type of things members here have done or would find interesting. They probably wound up on FB when their forums died.
If you ever come across someone doing something interesting encourage them to post it here. I think recruiting by word of mouth is one of the best tools we have to keep active membership. People come and go and it will always be this way. But to keep it alive we need new participants and that takes more effort on our part than it used to. People reach for FB groups since they are already on that platform and can find a group where they are already logged in. FB has the advantage of convenience. A case of easier beats better.
All this talk of membership reminds me to say how thankful I am for members such as yourself who have been here from the beginning or a good long while and still regularly contribute.