You described it in very negative terms, but I don't think it's necessarily that way. Humans are social creatures, and can't help it but judge someone they have no other information about based on the clothes.
If you're happy because you're dressed well, it doesn't have to mean you're "smug" - taking care of your looks shows that you care about other people's quality of interaction with you - everybody would rather interact with a person dressed nicely as opposed to if the same person dressed like a bum.
Also, there's something to be said about a confidence boost that you get knowing you're looking well kept. Most geeks will happily ignore all these points, but I think that's a mistake.
I agree that dressing nicely is a good way to communicate that you're serious about interacting with others.
You certainly don't want to come across as unprofessional and it's important to show others that you're putting forth your best effort (including appearance) for the work at hand.
If you're happy because you're dressed well, it doesn't have to mean you're "smug" - taking care of your looks shows that you care about other people's quality of interaction with you - everybody would rather interact with a person dressed nicely as opposed to if the same person dressed like a bum.
Also, there's something to be said about a confidence boost that you get knowing you're looking well kept. Most geeks will happily ignore all these points, but I think that's a mistake.