Is having a collection greed? Is it greedy to have a collection of material possessions (e.g. comics, stamps, etc.) that are not needed?
Greed is a negative (wicked) state of the heart (mind) were collecting money is not governed by moral standards especially with regard to fellow human beings (a key element is the employment of deception, for example). Also, a greedy person is not inclined to donate any of their money for those in need. In Luke 11:39 it is stated "And the Lord said unto him, Now do ye Pharisees make clean the outside of the cup and the platter; but your inward part is full of ravening and wickedness". 

There is nothing in the bible that indicates collection hobbies are greed (as long as no moral standards with regard to collection dealings are violated).