There are many different styles of art. A lot of non-artists dislike abstract art... Don't see it as something to understand. Most abstract art is not really meant to be understood. Likewise, a lot of paintings aren't meant to be of any recognizable object. It doesn't mean they're bad. It's just a different style of art.
As for the great historical works, eh, you'll find works from the big name artists throughout history are worth a ton due simply to the name they're attached to. You see this a lot with guys like Rembrandt. A painting will sell for $30,000 only to later be shown to be a fraud, making it worthless. If the painting itself was great, the artist wouldn't matter.
I'm a science guy who used to have no understanding of art, did not "get" it, etc, and then I took an art history class. I would by no means say I'm an expert of any sort, but that class really gave me an appreciation for art and its different styles. Abstract art actually became my favorite, and I think that class kind of unlocked my right hemisphere. Ever since that class I seem to have come to appreciate a lot of different things I didn't use to, and my whole way of thinking has changed too, like I'm less of a robot than I used to be. ...it's kind of hard to explain. Anyway, my point is to try not to judge, and don't assume there's really any "meaning" to a lot of art. A lot of paintings are just meant to be looked at. However it makes you feel is fine.
Like someone said, art is diverse as music. You might like certain forms, and if you don't, that's fine too.