OP, do not heed this advice. It does not work for everyone.
I can tell you that I have first hand experience of running a site for 4 years, moved to a new domain for testing purposes. And realized that there was nothing wrong with my previous efforts. In fact, my current site has grown so much, that if I moved it back to where I begun; my site gets a huge boost in visits. No rebrand necessary. In your case, a visiual rebrand is more necessary than a complete re-brand.
Especially if you have spent years working on the brand. It would be a BAD idea to restart all over again because it means losing
SEO trails. Losing whatever you had in search engines.