There are many advantages to using Google+: - Most notably, the audience is just much bigger, and the engagement is much greater because there is nearly zero friction to posting. I've been blogging for few years and G+ing (is that even a word) only since it came out, but I have ~40 subscribers to my RSS and ~1400 followers on G+. Audience is a big deal. People don't really use RSS. I get much more interaction on G+ than on my blog, and I like it.
- you and your (presumably good) content are much more discoverable, which allows you to grow your network and find more interesting people. It can also act as a nice easily discoverable portfolio. How often will a random person stumble by your blog? vs. How often will someone land on your G+ page? This will only become more and more likely as Google integrates G+ with Every thing.
- maintaining a blog has some weird connotations that I can't quite put a finger on. People sometimes ask me if I have a blog, and I always feel a little awkward inside saying yes. These connotations are somehow absent when I tell people I'm on G+. Maybe it's just the term and the way I hear it used, I really don't know.
I don't understand your concerns about who _really_ stores the data, or the like. Thank god I don't have to go through all that trouble just to be in charge of some text boxes on the internet. And so what if Google can use my posts to learn more about me and give me more targetted ads? I just see that as a win on my side once again-- I don't want to see mortgage ads on my banners or something.