Most who know me know that I'm VERY pro-suit. If I'm meeting a friend for a big mac, I'll show up in a suit (I might drop the tie in that situation).
I do think that the way you dress sends a message of your professionalism. I personally feel uncomfortable meeting with clients (no matter how close we are) in jeans. Like someone said above, if I met a lawyer or a financial advisor and they were wearing jeans, it does send a message. I am also pretty young for someone in my position (mid-20's), and for someone who spends his days telling people twice my age how to invest their money, they have to feel comfortable with me as a professional. I think if I wore jeans, I would add to the young image.
Having said that, I'm not against it to the point where I would avoid agents who decide to dress down. Two of my favourite agents wear jeans when with clients - but again, it's figuring out your level of comfort with the client. Dark jeans, shirt and a blazer is still smart but not as professional as a full blown suit.
I have been told sometimes when my clients meet me on a Sunday, for example, they feel uncomfortable when I wear a suit because they feel as though they are taking me out of my way moreso on a "day off" (whatever that is...). Again, on a Sunday, and if I'm feeling crazy I might drop the tie.
We have agents who show up in the office in sweat pants. I'm not being funny, but I sometimes wonder what they're thinking. Our office is located in a plaza and we do get walk in clients - what if a client walked in and asked to speak to an agent and Mr. Sweats was the only person here?