OK, I did it. Copied search.php to look.php, and blocked look.php in robots.txt as well as putting in the robots meta noindex, nofollow. Updated much code for my site to use look.php, and will have to finish that migration over the next few hours.
For search.php, I added code at the top that tries to find a proper brand or category page, and if found, 301 redirect to it. This is for any page request, not just Googlebot. If not found, the search.php renders as usual for now. In a bit, I'll add more redirection code to either 301 to look.php or handle the searches in other ways.
Now I have to update any and all precaching and reporting related to this.
Any other gotchas in terms of SEO I might want to consider at this point? It'll be interesting to see what happens in about 2 weeks with regard to Googlebot, other bots, and my site traffic.