I don't have space to keep all of my machines set up, but wish I did. I keep my Singer 15-91 set up for FMQ'ing, my modern Janome set up for appliqué and one of my FW's for piecing (I rotate between my 2 FWs). I just purchased a beautiful 301 and plan to put her in the cabinet that currently has a 101. The 101 needs to be rewired, but I have no space for her, so I will probably sell her and my Singer 328. Just out of room. Can't even leave my serger set up. My treadle has to reside in the great room.
i like to use all of my machines and not just let them sit around. If I were rich, I would put an extra room on the house and display/use them all!
if I were you, I would definitely keep both the 730 and the 831. They are both gorgeous!