That's a really great point, and thanks for the "Good Answer!" I particularly appreciate the duplicate content point.
What are your thoughts on the matter if the popular searches are not created automatically (e.g., could include "kitten" and "kittens" because those are perfectly reasonable search terms) but rather created manually? They reflect broad categories to help provide search engines a way of seeing important items, along with a site map. (All this is, regretfully, in lieu of a proper browse functionality that will require a bit more work given how the data is structured). Search pages would then reflect only orthogonal terms, such as "kitten" "puppy" "guppy" etc, so they are (at least as far as I can think) unlikely to produce duplicate result pages.
That's only my uninformed, amateur strategy. What are your thoughts?
Thanks!