I agree with you Robert, on the reunions thing. They're usually a cash-in.
The Police didn't need to re-form (and break their own vow to never do so). As much as I would love to see them, I suspect ticket prices and availability will be limited. To be honest I haven't read much about it, but why do they need to reform? OK, Sting's last 3 albums haven't been very good or successful, Andy Summers is now in mis mid 60s and needs a pension, and Stewart Copeland, is probably bored of earning little as a session musician!
But as long as a band can re-create their former glory, then I'm not totally against reunions, but generally, they're often past their best and it's more a need for income. Look at Genesis. I am SO glad Peter Gabriel didn't want to join them.
When a band are at their peak, or when artists collaborate, then yes, the results are often great and in some cases highly innovative. But like any working relationship, there comes a time when it's run it's course, and there's no point in tryinig to go back and recreate old glories.
Of course, my ranting point doesn't cover everything, and I'm not even referring to John and Billy. But for example a producer - if an artist has done a great, successful album previously with a particular producer and several years later, they agree to work together again, that's fine, and 9 times out of 10 it works. Look at Bowie with Visconti or Nile Rodgers.
I think with musicians it's often a different story. There can be a lot of conflict or disagreement - put any bunch of creative types in a room, and they'll argue, all wanting their idea to be the one. That's the way we are! ;-)
But I think when people stop working together, it's usually for a reason. If it was for a personal or conflictual reason, then they will always be hesitant to step back into the ring, as it were.