I have only raced for one season, but in my experience so far Wells Ave. is the best place to race when you are starting out. The pavement is in good condition and the course is pretty wide and safe (no crashes in the cat 5 race in my 6 races there).
I did not do Concord, but Wells is the easist race to hang with the pack that I have been to, the course is pretty flat and there is only one corner that requires slowing down for. The major chalange for a new rider is probabaly going to be the accelleration out of that corner and the little rise that is after it, but it is not that bad. With that being said, however, the pace is still 25 MPH average, so don't think that it is too slow.
As far as people getting dropped, I have never been, so I am not totally sure of the rules, but I am pretty sure that it is OK to try to hop back in after missing a lap. There do alwase seem to be a few people there who cannot hang for the whole race, and you do seem to run accross them still going around.
Anyway, bottom line, I would higly reccomend it for a new racer. The drive would suck from NH though.