I've just witnessed a repeating pattern happen yet again, to a friend of mine this time, so I thought I'd ask for opinions.
Scenario #1: Your site had remained untouched for over a year and received predictable amounts of traffic from Google only to be reduced in half when you make a site improvement(add some articles, improve some pages etc... nothing drastic and no changing urls, not even SEO changes).
Scenario #2: Your site had remained untouched for over a year and it receives a sudden loss of traffic. You improve it by improving existing content and adding new content only to then suffer another traffic loss.
Why does it seem like you cannot touch an older site without incurring a very real risk of losing the traffic your site has been receiving?
Simple: Google is reducing the total organic traffic on purpose. (And directing it to ads.) Any change is a good excuse to reduce traffic. Even NO changes results in reduced traffic. The pie is shrinking. For everyone. (But I'm not bitter :-)
It's not *just* content. You want to look at your site architecture, your navigation, your time on site, pages per visit, social shares, etc. Who's linking to you, and who you're looking to. How many of your visitors come back for more. Then you want to look at all that in mobile too.
Then you have to ask yourself if your site is really useful or entertaining or informative; if it disappeared tomorrow, would people notice, are you replaceable, would 15 other sites jump up to take your place and serve your community almost as well?