Do you still buy CDs?  Do you still listen to FM (or AM) radio?  Do you have kids?  Can you get a decent price for the BS4?  Is space at a premium?

I have kept my BS9000 with my BS5.  I still buy a CD from time to time and the immediate gratification side of me likes to pop it into the CD player without waiting to burn it.  I also listen to the radio from time to time - although most radio stations now have internet equivalents - at least they do by me, but sometimes my internet goes down...  My 11 year old daughter buys CDs that will never be loaded into the BS5 because I don't want MOTS to find them (it is too bad that you cannot keep MOTS away from certain music)...  and my BS9000 is worth more to me than what it would fetch in the open market.

Could I live without the BS9000?  Sure, but I have the space, it's paid for and is still a "classic" to my eyes.  The only downside is that the volume wheel doesn't work on the BS5 because BS9000 is the "audio master"... and I must press N.Music or N.Radio on the remote to listen to it - turning on the BS5 by touching it doesn't awake the BS9000 - I think the same is true of the BS4.

Stan