Why have a redesign?
Your website is your "shop front" to the world, and you would like to give it an elegant & debonair look, so that your website is portrayed in the best possible light.
With progressive and trendy changes in lifestyle and technology, a website that was built few years ago would be quite out-dated now. It depends on your business and the impression you want to create. Your site can be built professionally on a reasonable budget, with greater lifespan. Your websites has to be re-designed on a 2-3 year cycle.