I've used it in the past to do something a bit similar. I had a sort of "master account" that was installed on all domains and then a second individual one per domain. Piwik worked really nicely and gave the end user the ability to see a sort of "combined stats" as well as per-domain stats. We couldn't get GA to work in this way (I think that has since changed).
This was about two years ago now and I've followed the development on and off and it's certainly come on leaps and bounds. It's definitely worth some investigation for your use-case.
This was about two years ago now and I've followed the development on and off and it's certainly come on leaps and bounds. It's definitely worth some investigation for your use-case.