Import Progress and Replace Assets don't change a thing...

If you've created several menus from the same PSD file, Rich, I'm afraid there's no especially easy way to update them all at the same time from Encore. How Encore works is that each time it creates a menu, it creates a new PSD file in the Encore project folder. It doesn't matter if you imported the PSD file as an asset or a menu or from a template, Encore is always making a new duplicate file for each menu.

So the problem you're running into is that you've updated one menu, but that is going to have absolutely no effect on the other menus.

The only situation where "replace asset" would do something to a menu is if you have a motion background set up for the menus, and you replace the movie file being used. And then you would still need to re-render the menus.

For your situation, a good plan to change all of the menus at once may be to create an action in Photoshop that you can run as a batch on all of your files. This should work if you are making common changes, like swapping out the background or changing the font of text. It could be tricky for minute details, though, and you'll probably have to fix a lot of the menus by hand.