The sense of community will be dependent on the street you live in, your neighbors, and how active you are in talking w/ your neighbor. But MM as a whole, there are events throughout the year. It is an isolated area, so you can be left alone if you wanted to.
I don’t think 92121 is as good of a value as 92126 for the same house, since they rented for about the same, go to the same school, have similar HOA, etc. Especially if you’re looking for the 2000-2200 sq-ft range. I think access to PQ canyon is better on the 92121 side.