I'm a firm believer that the proportion of rubbish composed in any given period is a constant. The reason we don't hear a lot of rubbish from, say Mozart's day, is because it's been forgotten. Today's music hasn't gone through that sorting process yet. So if you're going to be hearing a new piece at a concert, you may not know in advance whether it's any good. And remember, "90% of everything is junk."
The other problem, of course, is that great composers are often way ahead of their audiences. Presumably the Eroica sounded like rubbish to most of the people who heard it for the first time, and we know the Rite of Spring did. Today even knuckleheads can enjoy both pieces.
So be patient and keep an open mind with "modern classical" music. I try to reserve judgment until I've at least heard the piece several times.