Sites get dated. There is no doubt. But even more important than dating is they fall out of communication.
Web designers built your first site maybe five to ten years ago. You may be rebuilding because your business has changed or expanded, so it is entirely justified. You may be rebuilding because it doesn’t attract nor capture traffic. So by rebuilding it with a web designer you might be doing a little more of the same.
Websites are organic. They require lots of input and outflow to be living valuable organisms. Buying a car off the show room floor to race at a track requires lots of changes and not just appearance. The new systems installed like stability, engine, transmission, exhaust, and intake, will not change the appearance much, but will be essential to winning.
Optimizing can have a big affect at a fraction of the price. At the most, the appearance of the landing page will need to be modified or for the same price one can add a new landing page template that attaches to the existing site.
Understand the end result desired before making a change.