You can stack them to your heart’s content. I’ve generally been getting free breakfast, some kind of free credit (up to €200!), a near guaranteed one category upgrade with potential for upgrades to suites on more of a throw of the dice kind of thing plus your night credit and points.

I’ve found every RC stay so far this year to be a much better deal via Virtuoso than booking direct. I happen to think that Marriott giving up all the profit with me no longer booking direct is crazy business on their part (the franchises will lose 30%+ of the value), but that’s obviously their preference.