Surely most collectors, collect what they like and what they can afford. Two variables there.
That was me back in the day...
Never understood owning records I did not like but it meant I had everything released on a particular label, but no doubt it happens.
A DJ and a collector can be one and the same, but no guarantee that having a great collection makes you a great dj, even though plenty may think that!
I remember reading an article about Martin Barnfather who had to sell some rare tunes to fund the purchase of in demand great tunes. Thats probably something most djs do unless they are super rich!
I'd agree that having say a collection of 75% of all respected original vinyl records ever played on the scene, is probably double the number needed from 1980.
Ed