Having worked in hotels for forever and a day I can tell you that there is no spoken or unspoken policy on upgrading based on attire of the guest. There is often a great deal of opportunity to upgrade based on occupancy, however. If the front desk agent checking a guest in has a bias toward nicely dressed guests you could certainly receive an upgrade...but even if you are impeccably dressed, if you act like a jack-... you will still get a dumpster view...from any agent.