Perhaps I'm not clear on what you are calling "PVA".
If you're planning to dilute white wood glue with water and paint that on your bare plaster, you're asking for trouble. That's because when you paint over dried wood glue with an emulsion paint, the moisture from the paint will re-emulsify the wood glue, and any further brushing or rolling will break up the glue layer and you'll just have a big mess on your hands. (On the wall, actually.) You need that wood glue to be either dispersed in the plaster or under the plaster where there's not as much moisture and the plaster holds everything together until it dries out again.)
In the few times where I've painted directly over dried wood glue, the result was usually a mess and my regretting having done it.
If the wall paper that's on the cove is hard to stick to because of it's smoothness, I'd save that PVA you have for some other purpose and use a sticky primer (like Zinsser's Bullseye 123) to prime that smooth wallpaper, allow to dry and then paint over that. Not all latex primers are equally sticky, so not all will stick well to smooth wallpaper. Zinsser's Bullseye 123 will stick well to darn near anything, even glazed ceramic tile.
