Yes, for a couple of reasons:
1) Base maps are just old. After 3 years (I got the game late), I'm just plain bored with the standard maps (even the bonus pack)...especially CTF Hoth!
2) I find a server but I don't have the map so I switch off full screen mode, so I can toggle to my web browser and I find a pen to write down the web site (or map name) then I toggle out of the game and do an online search so I can find the server's web site, download the map, and place the .pk3 into my base file and then I restart the game to load the map and go back and find the server I was playing on and finally, 10-15 minutes later I discover I really don't like this server's rules so I go find another server but I don't have the map so I....(I think you get the idea!).
3) You can make the maps TABBot friendly to show off the improved AI
I would say 1-2 maps of each gametype (CTF/CTY; FFA/TFFA/JM; Duel); 30-40 MB maximum. Hilts optional. Don't bother with models.