Dallas and Houston are oil flights. The oil companies pay peanuts for their blokes to fly Club, and the spotty oiks often dress as you describe.
If you're angling after an upgrade with no real basis for said upgrade, every little helps (i.e. wear something appropriate), but in reality, there's a well honed computer algorithm that selects the upgrade based on a number of factors. Dress obviously isn't one of them. Current operational requirements (e.g. moving people when an aircraft goes U/S), your standing with the airline, and ticket class/value being chief among them.
Not wishing to brag too much, but I'm a very good customer of Delta, so I fly First class most of the time despite tickets being booked at lower levels. As a BA valued customer, it was much the same. High value customers are what the airlines see value in upgrading. MOD must spend millions per year with all the airlines, but individual servicemen don't fly often enough to climb the pole. I'm sure there are some on say the F-35 program (in fact I know there are) who travel sufficiently frequently, but they will be rarities.