You've identified an important point: the value of "evergreen" content, which offers a growth path instead of requiring the publisher to start over when opportunities wither for datafeed affiliate sites, MFA scraper sites, or whatever the current fad may be.
However, there are some caveats:
- On the Web, the term "content" is often taken to mean "filler." A lot of people that anybody can write (or hire some $5-a-day freelancer in Uzbekistan to write) useful articles by the bucketload. In reality, the job is much tougher, and it certainly isn't an easy path to riches.
- Not every page has the same value, and just adding 1,000 pages to your 1,000-page site won't necessarily double your income. There may also be a practical limit to what you can earn within any given niche. For example, a travel site about North America might be able to support 50,000 profitable pages, but you might reach the point of diminishing returns if your travel site about Seattle exceeded 500 pages. (Which isn't to say that the second 500 pages about Seattle would be a complete bust; they just wouldn't earn anywhere near the income of the first 500 pages, assuming that you'd already covered the city's most important and obvious travel topics.)