I'm well aware there are exceptions to everything in life. I knew that from the start, and I no way meant to imply that my opinion was the 100%-truth. I'm willing to bet there are people out there who live and breathe music, and are surrounded by different artists ~16/24 hours of the day. I don't doubt that, at all. I would say you are of a minory, however - someone who has a lot of music for the sake of listening to it.
To answer your question; yes, I go for quality. I don't go out of my way to ensure I have audio-ambrosia, but I'll definitely shoot for the higher file size when I hunt for tunes. I can count the number of .M4A/AAC albums I have on one hand.
In my opinion, music library should be measured by number of tracks and/or length of all those songs. [Both of which are easily seen for anyone who uses iTunes]. As has been made clear, simply saying you have 50 GB can mean a few different things, depending on the quality of your music.