Is there any other possible use for a reward certificate for a free night to a category 1-4 hotel if the Marriotts that I am staying at in Monterey or San Francisco do not have category 1-4 hotels? In other words can I use the certificate to get a discount for a room in a category higher than 1-4?
I have not figured out any way to do what you want to do. HOWEVER, I have been surprised by what some Marriott Rewards agents have done for me in the past! It is worth calling and asking. I would approach it like "could I pay the difference in points between a Category 4 certificat and a Category 6 certificate?" If they say no, just ask if there is anything else they can do to help you? I would give it a try.
Nothing wrong with trying-i have had plenty of help from MR. However, according to the folks at Flyertalk, this is one thing that Marriott has held fast. Its been a challenge because of how many properties have moved up from a Category 4 to 5. (Likely due to these certificates because categories are assigned based on location and reward redemptions. When the world has a bunch of Cat 4 certs-theres going to be a lot of cat 4 award stays.)