"Even piping plover weren't local to the area until 20-30 years ago. A few straggled in, and the birders have gone berserk making them feel welcome."
Where are you referring too?
I don't pretend to speak for others, but my OPINION is that the first documented research of PIPL (Great Lakes and East Coast) is generally attributed to John Loegering, University of Minnesota, in 1992. It is cited extensively by NPS, USF&WS and ACE.
Doesn't mean that was the first PIPL appearance, but perhaps the first time that someone took enough interest to do the research. I think Audubon wrote of harvesting PIPL and did works with their plumage, but I have found no documentation of that, nor that it may have occurred in the East Coast range (more likely Great Lakes).
I believe it is accurate to say, with the migratory patterns, VERY limited nesting, poor reproductive success, high natural predation (esp. ghost crabs predation), and being at the extreme end of their range, that PIPL are invasive or, at least, poorly suited and poorly adaptive to CAHA and CALO.