If you regularly update content on your site, you will not be as likely to need an expensive complete overhaul of your whole site. The web design community has a phrase, “Re-align. Don’t re-design.” The idea here is that if you’re constantly making small tweaks to your site that help grow your community and meet your goals, this is likely to keep you site looking and feeling familiar so that when you update the style and content people still recognize your online brand. If you regularly update content on your site, you will not be as likely to need an expensive complete overhaul of your whole site.
If your site is completely outdated though, it’s probably best to redesign the whole thing. Indeed, with Google and other search engines incorporating more mobile into its search results you may want to consider a WordPress redesign to make your site look good on mobile devices. Additional, WordPress design trends come and go quickly and it is important for your site to give a professional and modern look. WordPress has made switching themes easy and without affecting the content of your site. Cumbersome switchovers are a thing of the past. However, keep in mind some things like sticking with the same general color scheme, keeping the navigation in the same place, or even keeping roughly the same content. It goes without saying that you also want to ensure that the site looks better.