Regionals do have spots reserved for rookies (and I believe for local teams as well, it would be horrible to register and find out the closest availible regional was 500 miles away) but small regionals are fun in two ways:
1) They allow you to be more active with your robot- more matches = more practice
2) less teams there = less data to memorize for scouting = more free brain space
Also, with less teams being there in the first place, the pits feel a lot less hectic when theres only 30 gone-wild FIRST teams instead of 60.
_Alex