It is not uncommon for companies that have had a websites for several years to give it a major overhaul. New graphics, functionality, more pizzazz and better user experience are some valid reasons to overhaul your site. One danger to consider with a site revamp is that your site could lose its search engine rankings if one of several potential missteps occurs. I have seen several instances where a overhauled website suddenly experienced a drop in traffic (and business).The drop occurred because the redesign actually caused the search engine rankings to drop on key search terms.
Including an experienced, knowledgeable SEO specialist on your web team is the most effective way to avoid problems. The specialist should be able analyze your current rankings and traffic sources and identify the critical search terms that you are getting traffic and to understand why your site is ranking; then help the team make decisions that keep your rankings or at least have a plan to address potential problems.
It would be ashamed to create that new and improved website only to find out that you are not getting any traffic.