Wow, so many comments!
Thanks loads, to all of you.

I'd be happy to play with any of you were we nearby!
EDIT:
I was trying Vallejo's Matte Acrylic varnish for this bunch. It seems to be a little more matte than the Windsor & Newton regular, but there were also noticeable issues with frosting in spots. I mostly fixed it with the second application, but I guess the W&N is ever so slightly better, even if I do have to do three coats. They might be very nearly the same.
Still, it's not ideal. I *REALLY* want to try the W&N
Galleria Matte (which is apparently a different, slightly better acrylic matte varnish). I found a place I can get Testor's Dullcote and the correct thinner for it, but I'm holding off to see if I can find the W&N Galleria first.
Right now, I'm able to use all acrylic without resort to enamels (an important concern given our abysmal ventilation here), so I'm really hoping I can find something good for this very last step.