The guitar is probably late-sixties, an Angelica 3854, made in Japan, I think it's a Harmony copy. Not x-braced. I don't think it's a matter of needing moisture, I think its just showing its age a bit, like me.

I think I'll put the tailpiece idea on the back burner, and maybe try lighter strings - and also investigate that Bridge Doctor idea as well. Here's the website for it - looks like it'd be fiddly to install, but it might be worth it.

I've just PMd mandotim for advice on that. Anyone had any experience putting one in a guitar? And how did it work out?