You don’t have to start again, but what an opportunity to audit and address your content. What’s still relevant, what needs updating, what’s not present at all?
You really should take a very strong look at your analytics where available – and if you don’t have any available, make sure they are on the new site.
Look at where your customers land, how they move through your site – and where they drop-off. If you have a page that people drop-off or bounce from regularly, then you need to start looking at why. All the little bits and pieces that drive you and your customers crazy can be addressed in your new site build.