CWL - I don't fish that are often anymore and when I did in the early 90s, it was usually at the Merrimack. As far as other spots, there are tons of inlets littering the coast of the North Shore that you can access & find less people fishing. Also, the bigger the river doesn't necessarily mean better. Look at a lot of the smaller rivers & salt ponds emptying into the bay...
Another thing to consider is a club like the Plum Islan Surfcasters:
http://plumisland.surfcaster.com/index.html