We have more clients wanted a faceted search, similar to what you are doing with Shop By so you might talk about doing a real faceted search instead of using product templates for it because of the performance issues using product templates. I had started out using Shop By on a site that had around 1000 products because they didn't want to pay for a third party and we thought performance might be OK because of the small number of products and it was really slow -6 to 9 seconds for filtering. I did make the performance acceptable(2 seconds for filtering) by decreasing the size of the InputValue in the ac_ProductTemplateFields table so that it could be indexed and changed the search source code (yes, they had purchased source code) so that it used = instead of like and that made the page fast enough. I think it would be even faster if there were separate tables for Shop By and the ac_ProductTemplateFields equivalent would have the InputChoiceId stored instead of text for InputValue. You could do that if you limited the InputChoices to use a dropdown in the admin instead of allowing a text field. The facets wouldn't be free text anyway, they would be limited to certain choices. For example, the language of a book could be limited to only specific choices and that way there wouldn't be any anomalies in wording either. Then you could include Category and Manufacturer and Price filters.
You could even include in it or separate from it an improvement to your search box where it shows top x products for the search in addition to suggested search terms. On of our developers did that for an AC9 site who wanted to get away from paying Nextopia and it's pretty slick.