The suit is definitely not merely a sign of fifties-ism human respect. That eighty year old man remembers a time when no one would dare go anywhere- even grocery shopping, even the beach, in sweats and a T-shirt. Our clothing reflects our inner disposition, all elitism aside. Even people who were dirt poor had special clothes for Sunday. It's not about being a fashion plate- it is about charity and respect for God.
If a man has the means to wear a suit, he should wear one. Would you go to a wedding in anything less? To meet the president? Maybe people don't even dress up for weddings anymore- it used to be insulting to the couple to show up in anything less than your "Sunday best."
A collared shirt should be the bare minimum for Sunday Church. A suit is not necessary, no, but you are in the presence of God and higher standards apply. The best that is within your means, without being flamboyant, should be what you wear. That's just a little social convention that comes as a remnant of Christian civilization.
Yes, standards have changed, but not for the better. I find it odd that you think a suit is "old-fashioned." It is still the standard for men's dress anywhere.