Over the course of my English major in college and my month long course studying Thoreau and Emerson while living within a quarter mile of Walden Pond, I have called Thoreau many, many names. Not all of them were positive either, but at no point have I ever considered him a snob.
I'll be honest here. I have never really liked Thoreau. I respect him, but I don't like (reading) him. With that said, as I get older, I have come to appreciate his works a lot more. I still think it was odd for him to live at Walden the way that he did, but I appreciate what he was trying to test. His call for people to simplify their lives is especially apt in today's culture. I think a lot of people would benefit a lot from simplifying their lives. Honestly, I would benefit too. While I think it odd that he lived on Walden Pond the way that he did, I never have thought it snobbish. He didn't completely cast off all interactions with people because he thought they weren't worthy of his attention. In fact he frequently came into the town of Concord to interact with the people there. Most notably were his interactions with the Alcott family. He was practically an uncle to those girls, and a much loved one at that. That hardly sounds like snob to me.
Thoreau's separateness isn't snobbery. He simply thought he had a better way to live, and he encouraged others to follow in his example. But he definitely did not dismiss out of hand anybody who didn't immediately agree with him. That's something a snob would do.