It may or may not help. Reason... If the buyer is planning to expand or work on the same theme, it may help otherwise say if you have made a site on precious stones and the buyer wants to sell gym equipments, buyer would have tough time in getting updated in search engines.
I completely agree with Karu here. Recently I adviced someone on minisites and I had completely missed the above thing. I am pretty much impressed with karu's deep thinking and knowledge. Many domains may have different intrepretation by different people so it may not help always plus it may add to buyer's problems.
@karu, its not difficult to update results in search engines, just make a sitemap.xml of your site and send ping to the search engine you wanna update your result with, the search engine will automatically update the results and the cache. if you dont understand what i mean then use the sitemap generator plugin for wordpress and see how it works the creation of sitemap and pinging the search engines(google,yahoo,msn and more) both tasks in one click!