If one reads the description of their boats that NC has on their website, it should be very clear what they are designed to do. In my opinion, they are not a "play-boat" and don't pretend to be. NC tells you straight out that their boats are straight trackers.
I demoed an Expedition before I ordered mine and I have to admit that it was not at all what I was used to. I was a little turned off with the maneuverability, but after considering all of the rest of the package, I took Doug's word for it that the NC can be handled. Maneuvering the Expedition requires a different set of techniques that one might never discover in a lot of other boats, but what an eye opener it is. I now use these techniques on all of my boats--what a difference.
The other side of the story is that when you set out to paddle from point A to point B, the NC's tracking ability makes it easy. The boat stays on course, so your paddle strokes can be even and if you stop paddling, the boat doesn't wander off. It can make you a lazy paddler with it's ability to glide. And when the water gets bumpy, the NC really shows what seaworthy is all about. It just sort of ignors waves from any angle, or all angles at the same time. I've been through some real wash machines that I thought for sure would get me wet, but the boat just seems to take over and you come out the other side without even the thought of a brace.
So to answer the question, the NC Expedition is a boat that I would say is designed for the specific job of putting a lot of miles under the keel--doing it fast, while keeping the paddler comfortable and dry. And yes the boat can surf and it does very nicely when the waves are big enough, but I would never take it surfing as in beach surfing. I think a shorter quicker handling boat is better for that job.
I haven't paddled an NC 15 footer (actually 15'-8"), but I would guess that that boat would do alright as a play-boat. On the other hand, I don't think that composite boats would be my first choice in a boat that would be subject to intentional abuse.