I think as we lost the Delaware Bay as a fishing destination entirely, the decline of other species coast wide, and limited open season for other species, the amount of people and boats targeting striped bass has gone up, while as a whole the amount of boats fishing may have in fact gone down. But I just look at areas that I surf fish for striped bass and I can tell you the number of people fishing for them has skyrocketed.
If you take Cape May out of the Delaware Bay equation I'd bet there are only 25% of the boats fishing the bay when compared to 10 years ago. There is only two party boats still in regular operation, both in Fortescue. And a quick Google search shows me less than 10 charter boats and I seriously doubt they run with any regularity. I never see them and my boat is still down there. Only looking at NJ side.
The flip side of that is, as you said, a lot of those boats have simply relocated and now target striped bass out of the coastal areas and or are trailering their boats to the Raritan Bay.
Look at the some of the head boats that target striped bass now when Sea Bass, Tog, fluke is closed. A number of those boats would have never even thought to fish for striped bass just a few years ago.
So my guess is boats and number of people fishing is down overall, while number of people and boats fishing for striped bass is way up.