“Google Photo Tools or whatever (hey, call it Picnik!) and a ‘share on G+’ option?” – Then what’s the difference? The photos are uploaded privately by default, the enhancement tools are there. If you want them to stay private, they do. If you want to share them, you can. I don’t see how making it a separate product makes things less confusing; if anything it adds unneeded clutter.
Plus is just the identity system that allows all of this information to be shared across all of google products, the social product is just a result of that ability.