I agree that Jack wasn't dressed up any more than he usually is. Ang Lee is really trying to show us the economic differences between the two characters.
True, Jack could have dressed down to vist Ennis as not to flaunt his wealth. Better yet, just to blend in more when they are together. But even during their time together you see Jack in New Jeans and nice new coats, hats etc. Ennis always in his ultra faded jeans, old coat and well worn Hat that seems to get more limp over time.
But this scene does show that Jack, even 8 years after the reunion, is still hoping they can be together! "I got the card about your divorce, so I figured that meant........" and he gives Ennis that puppy dog hopeful look.
Sigh... Poor Jack. Ready to give up his life in Texas for the man he loves.