I have a client whose website gets about 700 unique hits per day. However, there are a lot of problems with the site.
Among a list of improper coding techniques and xss vulnerabilities (that have been fixed), the biggest issue is the URLs are not SEO friendly at all. I believe a total overhaul of the site will put it in better health for the long run.
My fear is a new URL makeover will destroy any traffic coming from back links and cached by the search engines. I can do a 301 redirect via htaccess but this site has ~500 pages.
using redirects is usually the preferred method.