Roubaix - couple times a week, minimum.
TriCross - once or twice a week. During the summer I use it for gravel trails. When the roads are sloppy in early spring I throw road tires on it and use it instead of my Roubaix.
Secteur - lives on the trainer. Sees regular use during winter months.
Fantom Cross Outlaw - occasional commute and infrequent winter snow rides.
I think I'm actually at the point where I don't need/want n+1.