Welcome to the Marriott Marketing Machine (MMM for short.)

Basically, Cash+Points for Marriott is different than for all the other hotel chains. Marriott does NOT really allow for combining points and cash in a night stay. All it means is that if you have a 10 night stay and want to use points for some of the nights and use cash for the other nights, you can now do so under a single reservation. It does NOT have anything to do with off-setting some of the cost of a night with points while paying for the rest of that night's rate with cash.

With that said, on award reservations only, if a hotel has upgradable rooms and is willing to list them, you can get a reservation for an upgraded room using their "upgrade" certs (or cash). You will normally see this on beach resorts that have "Ocean View", "Garden View", and/or "Ocean Front" type rooms. You might see those upgraded rooms using the online reservation tool when looking for award rooms. You can also sometimes see them at some of Marriott's suite properties like RIs or TPSes.