I wasn't really talking about suit and tie though - sure, there are functions where everyone dresses up, even the most die-hard of UNIX greybeards. I also wasn't talking about making sure everything is clean (though it should be!)
I was talking about maintaining a more fashionable wardrobe (and there are many definitions of this, but t-shirt/jeans doesn't qualify under any of them) for everyday life. It doesn't have to be big, or extensive, but spending brain-cycles on dressing yourself is more often than not worth it.
Sometimes all it takes to open a door you never thought would open is well-fitted jeans, a well-cut collared shirt, and a broad smile. Or hell, sometimes opening doors is a flannel shirt, vintage t-shirt, and Converse sneakers. The standard geek ensemble, I've noticed, doesn't do much. Your mode of attire is a form of communication, whether we like it or not.