Which photographs matter? And does everyone have an equal vote?
There are no easy answers to these questions. At one level, the photographs that matter are those that a lot of people think matter. In other words, if a million people think that a particular photograph matters, then it's probably a more important photograph than one that only a dozen people think matters. But this over-simplifies because it assumes that everyone has an equal vote and that there is an unambiguous and quantifiable hierarchy of 'what matters'.
The problem is that 'what matters' is subjective. A community of peers may well have a clear consensus about 'what matters' but they can't expect other communities to agree with them. For example one community of photographers may believe that "Pepper #30" (Edward Weston) is an example what really matters, but a different photographic community may well say that "The Falling Man" (Richard Drew) matters more and that Weston's work is just a historical footnote.
I think that this is where the difficulties lie for people worried by the "sea of images" you refer to. When what matters to you is being swamped by stuff that doesn't matter to you, then you can't help but feel threatened. And it gets even more threatening when your livelihood depends upon other people agreeing with you about 'what matters'. People react in all sorts of ways when they feel threatened.