I googled around for some info on this boat. But, you probably already found most of this out by yourself. Natural Progression Kayaks was a fiberglass boat manufacturer in Sun Valley in the 1970's. Looks like they might have gone out of business around '77 or so. From the photos, this boat looks like a standard design that several boat manufacturers in the '70s and '80s produced. Most of them were likely based on the Lettman Mark IV or V slalom boat design from around 1972, with slight modifications to the deck lines. The internet tells me that the Lettman Mark IV was one of the most copied whitewater kayak designs ever produced. I don't doubt it. In the late '80s, when I started boating, my dad went out and bought three used boats for him, me and my brother to learn in; a Perception Mirage, a club made Mark IV or V, and Sawyer that had similar lines to the Mark IV. Even though the boat is around 40 years old, it looks to be in great shape. If it was stored indoors or out of direct sunlight, it's probably still durable enough to paddle. For $180, it seems like a good deal.
It's certainly not as "artistic" as some of the composite squirt and slalom boats that were made in the '80s and '90s, with crazy metal flake and day glow deck graphics. But, I wouldn't call it "junk". While this particular boat might not have a whole lot of history (it looks like it was rarely paddled), the design has a great deal of history. The growth and advancement of whitewater kayaking here in the U.S. owes a good bit to the imported European slalom designs of the early 1970's. I wouldn't mind having it, just to show a bit of respect to the "roots" and progression of the sport.
P.S. FSM, what model Phoenix do you have?