I know there's no single number to quantify this, but I really wonder what the signal to noise ratio on Twitter is. Sure, if you follow good accounts there are some gems from time to time, but it seems the vast majority of tweets are just complete wastes of time and resources, spraying out at a ridiculous rate.
For this to add value to Google SERPs, they're going to have to dedicate some real time, energy, and resources to process all of those tweets, something I think I wish they'd spend on other stuff than identifying which tweets are about someone's cat or not.
Twitter has a very good signal to noise ratio for me so far, even with images, videos and promotion tweets (which are all detrimental to quality).
Part of that success is the ease with which I can follow/unfollow people. It is often the second point of contact to people I met somewhere, e.g. conferences or other social gatherings.
That said I have just uninstalled the mobile app, because I got an e-mail promoting private messaging (why?) and get the overall feeling, that I am no longer the target demographic for Twitter (tech savvy power users that tweet themselves vs. mostly consuming VIP followers?!) since Twitter does much to worsen my experience (aforementioned imgs, videos, muting, etc.).
The signal to noise ratio from people you've followed is generally good, but the same isn't true of search from what I've seen - plenty of spam tweets there. That's probably only going to get worse if more people are going to see them.
For this to add value to Google SERPs, they're going to have to dedicate some real time, energy, and resources to process all of those tweets, something I think I wish they'd spend on other stuff than identifying which tweets are about someone's cat or not.