You could just overlap the circles. Have the "kitten pictures" circle if you like. Or make one giant circle instead.
I know you *could* but I think the culture on Google+ is such that that would be aberrant behavior. If I started posting kitten pics to my one giant circle, people would rightly say "Why are you posting kitten pics, I only know you from this game we both play, I don't want to see that crap." Because they have an expectation that I'm going to make use of the circles and segregate my posts. Circles are a key feature of Google+, and if I don't want to use them, I should go to Facebook.
On Facebook that culture doesn't exist. I've heard it's possible to do (friend lists?), but I honestly haven't even checked out the features enough to know. I just know that everybody posts things for everybody to see, and so people expect that. If some work colleague adds me, they KNOW they are signing up to see kitten pics and whatever other random stuff I post.
Also, even if I broke the mold and started sharing everything with everyone on Google+, that's only half the story. Others would have to start doing it to, otherwise the benefit I'm looking for (seeing more stuff about other people) wouldn't ever come about.
Google+ just isn't designed to share as much as Facebook. You limit who you share stuff with, therefore you share less overall. That's a fairly obvious result of what I think was a short-sighted design goal... designing a social network where the expected behavior is to share LESS... that just doesn't make sense.