> But I cannot notice a major difference between the $100 system, and say a $100k system (or whatever audiophiles spend).

I more or less agree with this but the main problem is that people listen in untreated rooms with horrible acoustics.

Once you hit that "medium good" threshold, which is pretty easy these days, more expensive speakers aren't going to make a difference until you get your acoustics under control.

If you do have a nice room, you will definitely notice the difference between the medium good setup and a nicer one, although you will hit diminishing returns WAY before you reach the $100k speakers.