My Collections took off in terms of interactions. Many more +1's. Many more comments. Much better interaction. However, my overall follower count to my profile itself dropped. I now have more subscribers to my Collection than I do my profile. I prefer the interaction though. It's much better than the interaction I get on any other SNS (Facebook, LinkedIn, Twitter).
On the Pages I manage things have been pretty static in terms of activity. Not much has changed there. I still post news and updates regularly, but people don't seem to interact with or follow those anymore. It seems Google is changing how Brand Pages work and integrate with other Google properties (Maps and YouTube in particular). It's necessary to have full profile information there, and to fill out all the details, but actual information posting doesn't get the return it once did.
Haven't created any Collections yet. Just haven't really explored the potential.
I do use Google+ in my social media cluster displayed from all pages on my site and post a couple images linked to articles each day. Not a lot of Likes but it does seem to be a steady, but low, traffic source.
One potential value there is the images/links get scraped & posted again by several social news type sites creating a bit more traffic.
I was always more concerned with the business ID role of Google+ and the effect it has on local business search, especially with Google maps.
Since I have the api coded into my responsive design, I'm a bit paranoid it will eventually be euthanized like so many other Google corpses. The business role helps me feel more secure about that.
I've used collections before, publicised it and gained some followers for that collection. Had a few comments here and there as well. I also frequent the Google+ Communities I joined recently. Some are active, some are not and some are just filled to the brim with promotions.