Personally, I'd avoid lockoffs ("guest room") at MVCI. Most FFI's I've stayed in are better. A master (1BR) is a bit cheaper than a Cat6 and a decent deal, depending on resort. That's likely what I'd go for, if targeting MVCI.
Socrates is correct about room management. We owners get first dibs. However, many villas are surrendered to Marriott for points as well as for rental and go into Marriott's room pool. Also, MVCI has many "developer owned" villas (unsold stock) which also are available. There is more flexibility there.
My personal opinion is to always book the standard room (revenue or points) and make any upgrade deals directly with the room manager/GM at the property after arriving and perusing their room stock. I've had enough negative experiences to now follow this process. Likely said somewhere prior, but points can only be used to upgrade a reward reservation, at least according to the T&C's...
Please note: you can only use upgrade rewards when you are redeeming points for a hotel stay; you cannot use upgrade rewards to upgrade a paid room.
https://www.marriott.com/rewards/usepoints/hotelrmup.mi
Pat