Is it worth making a few website improvements or completely redesigning the entire website? Depends...we chose website improvements.
Not all web designers are SEO specialists. When they are, you get an added bonus.
I am redesigning a new website for a client of mine. She has excellent rankings (i.e. #1 rankings) for a majority on some highly competitive keywords.
When redesigning a website, usually the name of the files or web pages may change or they will be placed in different locations on the web server. For example, let’s say the page products.html has the #1 ranking on Google. If this file is moved or it’s name is changed to, let’s say index.html and placed into the /about/ folder, your #1 ranking may disappear. Why? Because after Google and other search engines re-index your site they essentially have to start all over – from the beginning. In their eyes, it’s like you just launched a new site. So now you’ll have to wait (maybe forever) and work real hard to gain top position you once had. To avoid this easily, do not change or move files that have top placement.
If your site is currently going through a redesign and you have web files in top SE positions, make sure your webmaster/web designer understands the implication of making web filename changes.
Being a web designer is good, but being a SEO web designer is great!