In the past I've gone years with just one bike, just like I've gone with just one motor vehicle. It is nice to have a 4-door passenger sedan and a pickup truck and a 2-seater sports car all at the same time, but I can get by just fine with just one car (as long as it has a trailer hitch on it. Likewise I can get by with just one bike, but it is nice to have options. Currently though I have one car, a wagon with a hitch.

My Colnago Master Light has a BOB trailer skewer on it just in case I wind up with just one bike again someday. I've also got a MTB with a BOB skewer too since that one-bike-only day ain't quite here yet.

Multi-bike ideality:
1. Matching his'n'hers Raleigh 3-speeds.
2. Commuter converted rigid MTB.
3. Singlespeed of some sort.
4. Multispeed roadbike.
5. Touring bike.
Any excess can be considered as flip/swap fodder.

Currently I have redundancy and haven't sorted out the overlaps.