I am sure if you have ever been to a classical music concert, the question of what to wear naturally arises. For the last concert I attended, my mother was quite worried as to how she should dress. I had taken her and my older sister to the opera previously for which they dressed up, despite their seats in the second balcony (I sat in a boxed seat), but this was slightly different. Although all due respect should be shown to the performers, it ultimately was a concert performed by advanced college students and some older musicians waiting for their big breaks. The audience consisted of the performers' college buddies and families, with others who knew the value of a dollar interspersed. Concert tickets literally cost a dollar.
I told her to dress comfortably with casual shoes because we had to walk from the train to the concert hall - that should take precedence over anything else. Despite the resolution of our issues, sitting in that balcony recessed into the back of the hall allowed me to see the oddest mixture of clothing styles assembled outside some fashion show. There were over-eager young couples, most on promising dates, dressed to kill, making sure everyone took notice of their wealth and style. Well, at least their style, the big spender laying out the grand sum of two bucks on the evening's entertainment. Others, mostly older people, look liked they paid a dollar merely to get out of the wind of Chicago's claustrophobic downtown streets. They looked disheveled and made lots of noise opening candies and digging in what seemed like plastic bags. I wanted to kill that lady. There were overly polished gay men with every hair follicle carefully gelled into place and squirmy kids with jeans (my nephew).
As you can see, people are very confused by what a concert of art music requires clothing-wise. I think it depends on why you went to the concert in the first place. If you are there to be seen while ignoring music, then by all means, wear that wedding dress from your second marriage that you have been dying to use. If you like music and are not necessarily there to find your third wife or husband, then dress casually and comfortably because these concerts can take a while. And if you are a rich bastard that buys expensive tickets to concerts so you can take a nap in dark, air conditioned buildings with nice mood music playing in the background, wear what you like - we can't do anything to stop you.