Design is the part everyone can see, so it is easy to look at a dated site and assume the whole thing needs replacing. Sometimes it does. Sometimes the useful parts are still working perfectly well.
A site can look tired while its page structure makes sense, forms work, important URLs are established and the content is mostly accurate. Starting again in that situation may create work and risk without solving much.
The opposite also happens. A site can look reasonably modern while years of additions have left the navigation confused, pages duplicated, forms unreliable and every small update harder than it should be.
I would decide based on what is actually broken, not how old the website looks.
Keep what still works
A redesign makes sense when the foundation is usable.
The business may still offer roughly the same services. The important pages are in the right places. The platform is stable. Customers can submit an enquiry. The main problem is presentation, clarity, mobile usability or the journey through the site.
In that case, preserving the useful structure can save time and avoid unnecessary disruption.
You still need to be critical, though. Keeping the old website should not mean protecting every old decision. If the copy is weak, rewrite it. If customers cannot work out what to do next, fix that. If the mobile experience is poor, that needs proper attention rather than a cosmetic reskin.
Rebuild when the old structure has become the problem
Starting again becomes more sensible when the site no longer matches the business.
Maybe new services have been added wherever there was space. The same information now appears in several places. The enquiry process is unreliable. Nobody is sure which plugins or integrations are safe to remove. A simple content change turns into a technical exercise because too many things depend on the old setup.
At some point, continuing to patch that structure creates more compromise than a clean rebuild.
This is why two equally dated websites can need completely different projects. One may need better design and clearer content. Another may need its structure, technology and enquiry process rebuilt properly.
Be careful with things that already have value
Search is one reason I would never treat a rebuild as a blank slate.
An existing website may already have indexed pages, backlinks pointing to particular URLs and search visibility attached to its current structure. If URLs change, Google recommends mapping the old pages to the new destinations and using permanent server-side redirects such as 301 or 308. Google also notes that rankings can fluctuate while a moved site is recrawled and reindexed.
The same care applies to analytics, forms, tracking, integrations and any pages that already bring in useful traffic.
A new website is not an improvement if launch day quietly breaks parts of the old one that customers were using.
And sometimes the problem is not the website at all.
If leads are already coming in but nobody follows up consistently, changing the homepage will not fix that. The failure is further down the customer journey. Rebuilding the site may feel productive, but it does not address the thing actually costing the business opportunities.
How I would make the call
I would look at the website as a whole: how well it represents the business, whether the structure still makes sense, whether customers can take the right action, whether the technology is maintainable and what happens after someone enquires.
If most of that is working, improve what is there.
If the site has become a collection of patches and compromises, starting again can be cleaner.
At WeDevelop, we do not assume an old website needs replacing just because it is old. A website review should separate cosmetic issues from structural ones before the scope is decided. That makes it much easier to see what is worth keeping and what is getting in the way.