While the thread you point out isn’t a random sample (self-selecting and what not), I would bet that it’s the most representative one you’re going to get.
So I think it’s safe to conclude that the average # of unicycles/uniclist is very close to 3.
Although, thinking about it further, that self-selecting aspect would most likely bias the results towards the more active members of this unicycle community which I would guess covaries positively with number of unicycles. So a case could be made for a smaller average number for the full member list.