Google will give better ranking to sites that update their content regularly or refresh a page.. However, as that content ages a little, the ranking will quickly deminish. If you are lazy, you might like to consider that after an even longer period of time, the content will again begin to rank more highly, as the content is considered "stable and authoriative"
Just changing a date or something minor is not enough. In general, you should only give this rule as much consideration as you give your own customers a reason to come back. eg don't just change small sentences, instead make your website a vibrant source of news and information where your customers can come back to time and time again to learn more about your products, services and your industry. Add testimonials from happy customers, discuss new uses for your products, and reviews of relevant products.
The more content you have (aka the more pages) the greater the potential "net" you have to "catch" new customers. More content is much better for SEO than few pages that change often... Keep your old news stories on the web, as these are often great places to catch new customers. Not everyone will visit your website via your home page, in fact around 50% or more of search engines will direct customers to pages deep in your website.
Regarding time, a really important factor of website ranking is the age of the website and the age of the domain. So keeping the same domain name for a long time is a good way to get your website higher ranking... however, before you go and buy yourself an "old" domain name, google are smarter than this.. if the history of the domain name is not relevant to your self or your industry, then they will probably reset the value of that domain name... Basically the idea is to not change your domain names half way through the game, and not to do any tricks... stay with the same horse so to speak.