At the risk of being accused of taking this more seriously than I should I think we need to remember one of the reasons that aircraft crews wear a uniform. It's to give them authority and to be easily identifiable - things that are very important in the event of an emergency when the pax need to be told what to do.
Us poor controllers need to have authority at times but we do it with our voices rather than through appearace - hence appearance doesn't matter for doing our jobs.
I personnally favour the relaxed mode for the ops room, it's just more comfortable. In the past, however, I worked for one mob whose ops rooms were an embarrassment with tatty furniture, sharp edges to furniture etc. I chose to dress in older clothes there because they would often get damaged. Strangely, the management encouraged smarter dress because they sometimes brought round 'tours' of the local Rotary Club or Womens Institute and felt that shabby controllers did not reflect well on the outfit (if you'll excuse the pun). It never seemed to occur to the bosses that an ops room with holes in the panels because equipment had packed up - sometimes with wires hanging out of the holes - and chairs that were so worn that the stuffing was coming out had more effect on the public perception than controllers in jeans and open-necked shirts.