Perhaps not its intended purpose but to me it looks like an upgraded version of Google Keep. As someone who likes to collect resources and notes on topics for both research papers and personal projects I see this as a useful tool for that. I don't imagine any of my 'spaces' having more than one or two other people in them.
In reference to all the 'Google will kill this soon' posts. I agree there seems to be a growing list of discontinued products but their Takeout [1] service almost always lets you get your content out. While things like social interactions on G+ might hold value on the platform itself, as long as I have my notes/photos/data at the end of the day, I am happy to treat these products like I would a text editing app, just a tool to work with the data.