I always wanted two bikes minimum when I was an everyday commuter. One "primary" bike and a second "winter/rain/something's wrong with the primary bike" one. The last thing I wanted when I'd get up in the morning to go was to find a flat and have to think about fixing that and being late; and though the primary bike would be ridden in the rain when rain was unexpected, primarily dry riding extended the lifetime and maintenance intervals on the primary bike.