I live a short ways from a town in south central indiana that has lots of artists and thus lots of galleries. I've bought (probably) twenty or thirty paintings. A couple are phenomonally beautiful. (stare at them and get lost for a few hours type beauty) others are merely pretty. But all were worth the money. That is great art
Now your "sofa" comments have more credibility. But how many sofas do you have??
I guess my personal standards for great art are that it must show greatness in some or all of these areas: beauty, skill, the ability to communicate or evoke an idea, thought or emotion, the ability to touch one's heart at some fundamental level. I think I'd say that for me, great art has to have any 3 of those qualities.
However, I think time is the real judge. 'Course, on the contemporary stuff, I'll just have to settle for using my own standards.
I'm impressed that you own so many paintings, very cool.