This is a bit embarrassing, but I just found a cool “new” feature in Yukon that turns out to have been in AS2K all along. (The fact that it was not documented is no excuse for not knowing it.)
The Descendants function can take a Set (as well as a Member) as its first argument. So, for example, if you want all the leaf level Road Bikes and Touring Bikes, you can just use Descendants({[Road],[Touring]},,LEAVES). It’s very handy.
And you don’t even have to wait for Yukon to get it. (You just have to wait for Yukon to get it in BOL.)