There are two different things here: appreciating art and paying big bucks for it. Ignoring the subjective nature of beauty, is there some law that says art should be beautiful?
I suspect some do, and some don't. Why don't you ask them or read what they have to say about their works...
There are three candidates for me:
1720's: Vivaldi's Four Seasons, Bach's Brandenburg Concertos and St Matthew Passion.
1790's: Mozart's Requiem, Beethoven's Pathétique and Moonlight Piano Sonatas.
1870's: Wagner's Ring Cycle completed, Brahms' First Symphony and Violin Concerto.
I don't to listen to music anymore, but when I did, I was almost exclusively a classical music fan. Almost anything by Bach, Vivaldi, Mozart, Beethoven, Brahms and Mahler will satisfy. Don't restrict yourself to symphonies, though. Trios, quartets, sonatas, concertos, etc should be the targets...