My (French) spiritual director once told me, "do what the others do." (referring to my fellow seminarians).
Applying this to dress, I should A) dress as well as I ever dress when going to Mass, and B) I shouldn't stand out, as if I'm somehow more important, rich, famous, etc.
People my age (low 30's) don't normally wear suits. I'm from a very "informal" generation.
Moreover, my regional culture comes into play. In Texas, if you're worth millions of dollars, you'll probably still go to fast food restaurants, wear a hawaiian shirt and tennis shoes -- and a person talking to you would NEVER guess your net worth. It's a Texas thing, I guess.
In New York, a similar rich man would be wearing nice suits, a Rolex watch, would have a nice car, etc. Not so in Texas.
Weather might play a role -- in Texas, it's hot about 7 months of the year. Wearing a heavy coat just isn't that appealing when it's in the 90's (or 100's) for months on end. The culture adapts to deal with this fact.
With all that in mind, I think "dressing up" for Mass is appropriate, as long as you're not looking ridiculous (most formal would be dressing like you're going to a wedding -- black tuxedo and bowtie, etc.). In other words, both you and those around you should know that Mass means something to you. You shouldn't ever look nicer than you do when attending Mass.
For what it's worth, I always wear a button-down shirt and tie, and khaki-type pants (white, beige, or black). I dress better than most of my peers, from what I can tell. If I wore a suit coat I'd only have company with men 2 (or 3) times my age. In my book, that would qualify as being eccentric.
I have a (cheap) suit coat that I bring out for Mass on Christmas and Easter. Other than for those 2 days, it never gets worn.
Dinner date? I don't even know what that is. My wife and I are very down-to-earth and practical, and we were the same way when we were dating. Our idea of "dining out" for a special occasion is going to a sit-down Mexican restaurant which costs $20 TOTAL.
Anyhow, I'm not from Texas but I really fit in here with my down-to-earth upbringing and the common sense I have (thanks to God and my parents). Texans are all about being down-to-earth and informal.
If it helps, I DO feel dressed up when I walk into a store in my "church clothes". I feel like I'm advertising that I've been to Mass recently.
I'm not very fond of suits either. I also think they are way too "generic" and "establishment". I'm not a punk, but I could have been under different circumstances. I sympathize with the punk movement, since they were justifiably upset with what they saw as a culture-less, vapid (empty), banal, conformist society that would take away their humanity and individuality.
I can understand why someone wouldn't want to be "just another brick in the wall".