On the other hand, infrastructure can only be as useful as the applications they support. Technologists love solving hard technical problems [1], but ultimately, isn't the main goal to improve peoples' lives? Almost all the engineers I know would prefer to work on sophisticated interesting problems than "another web-app," but there isn't much point if it is just for our own edification.
I can understand your disdain for Instagram's frivolity, but people said the same about Twitter and it ended up playing a major role in the Arab Spring, whereas almost no one outside the techworld knows or really cares who runs their infrastructure. Of course without this infrastructure it all wouldn't work.
Like you say, comparing the two is like comparing apples to oranges, you can't really argue one is fundamentally more important than the other.