The Galleria is just a big mall, and you can find the Cheesecake Factory anywhere. I would skip it.
Also skip the Museum of Science unless you'll have kids with you. I loved it as a kid, but when I went a few years ago, it was totally not what I remembered. It's oriented towards kids. Of course, you may want to go to Omni Theatre, but that's all I would do there.
The bums at Harvard Sq. aren't mean. A lot of them have talked to me, and they never ask me for money. Of course, I don't have a job and would be a bum if I wasn't married!
Have a great time!