I think that PS+ is fully worth the money if you have it, the exclusive 1 hr trials, the discounted prices, the free offers in the PS Store, etc. make it worth it for now, plus you get auto-dl's and soon cross-game chat as well, but cross-game isn't enough of a reason to get it: you can do it even without PS+, just a + member has to host it.
Ultimately, if you were going to get Qore or something, then screw that and just get PS+, if you never spend a lot on the PS Store, maybe it isn't for you, but there is no doubt that you can and will ultimately save money with the service.