It just depends on your interest, the space you have and your philosophy. My older brother passed away a couple of years back and had thousands of CDs on classical music in his apartment in New York. While I was fairly sure a few of them might have been fairly rare, I didn't have the time and money to spend an extensive time going through them and I had to let them go for probably not near what they were worth. I felt bad, but I was up against time and distance (I lived 3000 miles away).