Google's John Mueller responded to a question in the Google Webmaster Help forums about changing a site's URL structure completely.
The site has tons and tons of dynamic URLs that look like this:
You get the idea. The site owner wants to change them to /boats-for-sale/fairline for example.
Now, for the most part, I am always wary about changing a URL that ranks already. John from Google said:
I'd recommend *not* changing them, if you'd just change them for SEO reasons.
But in this case, /search? might make sense, and I may argue with John. But I don't have the analytics or data to make a full decision on this, but typically /search URLs might signal the wrong message to Google. Even though Google wants you to feed them dynamic URLs as dynamic URLs and not as static URLs. But in this case, a search URL is something Google likely wouldn't want to index.
Forum discussion at Google Webmaster Help.