I've conducted a research in my DB and articles pre-2010 not having almost any hits.
We've had the opposite experience: Some of our most popular articles date back 10 years or more, probably because they've acquired a good many links over that time.
Regular updates can keep an article relevant, and some topics are "evergreen" and up to date even if they're left alone. (For example, a decade-old article on how to fry fritters or the life of a 14th Century saint probably wouldn't need updating very often unless tastes in cooking oils had changed radically or new historical facts had come to light during the last 10 years.)
Also, the structure of a site could have an impact on how much freshness matters. Is the site organized by topic or category, or is it in reverse chronological order, with older articles or posts being shoved to the back of the queue? For that matter, who's to say that Google may not weight "freshness" differently (if at all) depending on whether a site (or page, for that matter) is perceived as being a blog, a news site, an evergreen information site, an e-commerce site, or whatever? We have no idea whether that's the case, but it would be a reasonable approach.
As for the question of whether to use date/time stamps, that probably depends on the nature of the site and the content, too. For an evergreen article, a "last updated XX/XX/XXXX" line at the bottom of the page may make more sense than a time or date stamp, if it's needed at all. (That's the approach used by Wikipedia.)
