I have cut a couple sheets of the brushed aluminum into myriad little pieces while developing a project (that I will post eventually, no really). It cuts and engraves just like any other acrylic. I have optimized settings for it in my spreadsheet that I think are basically the same as medium Proofgrade acrylic. This is the wrong forum category for sharing them but, can do it in a linked thread, if you like.
I also have some of the copper stuff that I have a plan for but, haven’t got to yet.
They pass pretty well for their nominal metal equivalents visually.
The acrylic seems kind of thick for bookplates.
While paper stock surfaced with foil doesn’t cut well, there are metallic stocks that do. For example, Neenah Paper Stardream in Copper, Bronze, Antique Gold, Venus 2.0 or Saturn 2.0. It’s available in 105lb cover stock, which is pretty rigid.
I am not sure how practical it would be for your application but, you could also paint something after cutting. Molotow’s chrome is a dead ringer for a polished silver metal finish, for example. It comes in a pen but, you can open the pen and, put the paint in an airbrush or other applicator. They also make a gold (which I haven’t tried) that you might be able to blend with something (like green) to get a brass.