I'm assuming those certs are from a CC? If so, I doubt Marriott will exchange them for points. If you can't use them, maybe you can invite some friends to come visit you and put them up in a local Marriott?

Another use for "lower cat" certs might be for shoulder nights on a vacation. I drive the family to Destin each year. That is a long day drive (13+ hours). So it is nice to break that up into a two days. There are numerous Cat. 1-4 hotels around the half-way point between Dallas and Destin. Also, if you fly somewhere, maybe there is a Marriott close to the airport that is a Cat. 1-4. Those can be nice if you have a late arrival or very early departure flight.