I am in the same boat. My thoughts have been as follows:
1 - Keep the one most used: This is the Zeiss Ikon for me.
2 - Keep the one capable of the highest quality: For me that is my 8x10 Deardorff.
3 - Keep one capable of macro and telephoto: This is my K1000.
4 - Keep d...l, which we will not discuss here.
These are the ones my head tells me I can make do with. Unfortunately I have not been able to get my heart to agree.