judging by the number of sets for sale here, do you think the market is fairly saturated right now?
Not sure what you mean by saturated. The makers I know personally all have waiting lists running into years. No one seems to be backing out. It is good there are used sets available; instant gratification. As there are a large number of makers these days, there are also a number of folks who have given it a try but want to move on to something else. Were the market saturated, the wait lists would be getting shorter which does not seem to be the case.
I think it’s great that people who own sets they aren’t using are passing them along to someone who might. That’s how I got mine!
I don’t think there are so many sets around… or maybe is it just I can’t find one that interests me 
In my case, I’ve sold my Bruce Childress full set body recently, because I like to have now a full set body from Andreas Rogge with a A-drone. Now I live in Germany and it’s easier to me getting reeds, for example, directly from the maker just driving in his workshop.
It wasn’t that long ago that if you wanted a set of Uilleann pipes you played the set that you could get, rather than the set you may have wanted. These days players have the option of choosing from a wide variety of makers and available sets. In that sense Uilleann pipes have just “caught up” to other types of instruments in terms of accessibility. I mean classified ads everywhere are full of guitars, yet they still make new ones. Pipe-makers wait lists are full because now players would have had a chance to test out many different types of sets and have settled on the one they really want.
I remember in the early 2000s, maybe even up to 2008, demand was much higher, and so more people started making. I think this was due to a combination of things, mainly a reasonably strong economy, with more disposable income (the Feel-Good effect), but also a strong interest in Irish culture and music (the Riverdance effect).
Then the financial crisis hit, disposable income fell, and demand tailed off. Interest in Irish culture also waned a little. But you still have more people making pipes today than in, say 2000. So we’re probably going to have a healthy second-hand pipes market for a while until demand picks up again.