I think PS+ is very profitable for Sony, the Publishers and even the gamers.
I'd love to see some official numbers how many subscribers there are. Let's say there are 3 million people. In the EU it is 65 Dollars a year, but lets just say 50 Dollars p.a.
So that's a total of 150 million USD. And what they basically do is giving money to the publishers for their games which don't do very high numbers anymore. I mean, how much money do they have to invest to giveaway a game like Bulletstorm which sold like 400k on the PS3. That shouldn't be too much, maybe like 1 million USD. Peanuts for the PS+ money pool, but free money for the publisher. The only really expensive deal was Red Dead Redemption, i think Sony had to pay good money for it, since it is a real blockbuster and still sells well.
PS+ is an awesome value for the gamers, and everyone should participate. Heck, the more people get into it, the more value could be added (to sonys wallet, too).
must-have-list for platforms i don't own yet:
WiiU: Donkey Kong
XBone: Dead Rising 3, Ryse