No. Many sites at the top of Google, Yahoo and Bing have not changed in years and if your website as unique and valuable information you don't need to keep adding to it for the sake of adding.
It is better to spend your time carrying out other SEO work to strengthen what you already have and a good place to start is with the 20+ point checklist on the page Plan your SEO process
What's the difference between White Hat and Black Hat SEO?
How long does it take SEO to work?
Why am I getting lots of visitors but no sales?
Should I outsource my SEO to India?
Should I use a paid text link programme?
How much should I spend on SEO?
Where can I find a SEO certified company?
Are there search engine optimisation courses?
What search engine optimisation tips are there?
What is a SEO friendly website?
What is organic search engine optimisation?
Should I add a blog to my website?