Few people save brochures and then periodically reopen and reread them cover to cover. The same is true of web sites: If nothing ever changes on your site, hardly anyone will revisit it.
You can refresh some of the graphics periodically, but it will probably cost too much to change out large quantities of new graphics over time. Text, however, can be readily and easily changed at regular intervals. Your best bet: Change both text and graphics at a reasonable pace and at regular intervals.
Your site is never truly "complete" - make periodic changes to keep your site fresh and interesting.