Sure the number of players that are "good for" any given map might vary based on things independent from the map, such as the game play of a server, players' skills, players' sense of fun, etc. However, experienced Tremulous mappers, as well as players experienced with various Tremulous game plays, can make a rough determination on if a given map would generally work better within a given range of a number of players than other ranges.
With that said, I'm more interested in seeing quality maps made and played, and then individual servers can make the determination based on how well the maps play on the given server with various numbers of players on what the preferable range of number players would be for a given map on the given server.
I should also mention that while through a period of time on the GrangerPub server each day, there are matches that generally have less than 10 players, there is a peak time each day that approach 30 player matches ( or even above). So maps that are "preferable" for a larger number of players are practical on GrangerPub with the current player base. Also if things go well for Tremulous in the future, hopefully there will be many highly active servers.
As I have mentioned, there are already a lot of existing good quality "mid to large" Tremulous maps to choose from (don't get me wrong, more quality maps in that category for Tremulous would still be awesome), but not many good quality "small" Tremulous maps at the moment to choose from. The bottom line is there does exist a need in Tremulous for more good quality original "small" maps as alternatives to atcs, and that are not based on atcs.