While I do believe it can get relatively crowded at times, I do not think motorboats are allowed within the boundaries of the wilderness waterway.  If you want to have an outfitter fly you in, you have to land outside the boundary, and canoe in.  Float planes land on a pond or lake upstream of Alagash Lake, and you would then float the stream down to the lake, and continue down the waterway.   The waterway ends about 5 miles upstream from the town of Alagash, and motors are allowed only up to the boundary line, as far as I know. Things may have changed since 82, but I doubt that they have changed that much.  There are 2 or 3 rangers who live inside the waterway.  It may be that they do have motor boats? but my guess is that no one else is allowed to have a motor within the waterway.  

Here is a post someone made on paddling.net.  It was dated 7/4/04.  Though they didn't say when thier trip was, it seems to have been shortly before the 4th?

"Allagash River ME"
"In this day of reservations and quotas, this is one area that requires neither...moreover it seems each year its less used.
Used to be quite the populated canoe route 25 years ago..not any more...more moose than people for sure.
Perhaps its irrational but I know that the department that manages the area is running low on funds and I fear that the campsites on it will not be as pristine as they once were..and I wonder how long the ranger will be able to run a portage service.  However this 100 mile route will still be there!
We had a six day trip and saw seven other folks."