Rich, of course, is absolutely correct. While there have always been a hard core of collectors that appreciated the NE fowler there have never been many of them and, at least here in NE, they tend to know about each other. I'm reminded of a story told me by the late Don Andreason, one of the small number of collectors that did appreciate them as early as the 1950s. A gentleman was offering an extremely early (17th century) fowler with a slam-dunk American provenance for sale...this is the gun now known as the Thompson Fowler and I believe it's in the Smithsonian. At the time he showed it to three different collectors with what was a stupendous asking price. (He clearly knew that it was extremely desirable) All three declined and made an offer...and all three offers were very close. Don was the last of the three...until then he hadn't seen it and didn't know who had but the seller exploded in frustration with "are you guys all in cahoots?".
I'd say the same is true for NE rifles today. I think I have 15 or 16 of them. All of them are the fairly plain, run of the mill versions and only two of them are in original flint but the most expensive of all of them cost me $1000. (I think there are two of those) All the others cost less.