The brother who chooses to dress as if a Lodge meeting is a casual social affair has lost sight of what makes a Mason a Mason.
I think this depends on what's going on. On degree nights, I personally like the idea of dressing more seriously, because I feel like the ritual is serious. We get maybe four hours over the course of three nights to take a good man and make him better by our ritual. We must then be very serious about the labor that we are about during those four hours or the job won't get done. However, for stated meetings, most of what's accomplished is just enjoying each other's company, and if a man is going to go have dinner and fellowship with his friends, it's natural to want to feel comfortable. Again, I think it's different for officers because they are more "at labor" than the other brethren, but I still don't feel it's as serious as a degree.
I like the suggestion by JohnnyFlotsam that a man should wear his best, whatever that is. I would probably add the caveat that a man should show respect to the expectations of those around him. I personally dislike feeling out of place. I enjoy wearing suits to lodge because dressing up for lodge is part of my feeling that it's special, and, despite going almost every week, it still feels special to go to lodge every time. But, when I visit a lodge for the first time and find out almost no one else is wearing a jacket, I feel out of place and awkward. No one makes me feel unwelcome, but I feel like I'm behaving badly. Whether you're overdressing or underdressing, it's not polite, and if you're out of place by enough, it's distracting.
I think flexibility is the key. Flexibility of lodges to take men as they come, within reason, and a lodge to expect a brother to fit in, within reason.