Whenever there is a must-buy game or when it becomes affordable. I wouldn't be diving head first even for one must-buy game, a 500 USD pricetag is huge whereas you can always buy a Nintendo 64 and Goldeneye 007/ Super Mario 64
500 dollars? (Approx. 305 GDP) Not worth it; get a PS4 or wait for a sale. The PS4, generally, is about 400 dollars. (Approx. 244 GDP)