With hindsight I should have reversed the ratio. Two of the guys that came on the mat were clearly interested in a more competition-oriented experience, and I was able to suggest some other classes that would probably suit them better.
Happily, my class seems to be going through a transition from very small to a thriving smallish group. I hope that people continue to find my class, but there are limits to how fast I can grow it.
Also, for some -- especially those who want or expect a primarily competitive experience with lots of randori, sparring, or rolling -- my class has little to offer, and this should be just as apparent from watching, as participating.
While in the past I was keen to get numbers up, it seems that I am now experiencing the opposite problem.
So a new policy is needed: Until I have a good chat with a prospective student and determine to let her or him on my mat, my new policy will be to ask that they watch rather than participate. Especially when a heap of newcomers turn up all at once!