jamesdak 

I think if you are serious about your riding then yes you do need at least a spare. When my Trek broke I did not have a backup. But within a few days I did. And then I picked up yet another nice older bike. The Trek spent several months (got it back just today) at the LBS waiting warranty so I used one bike as my main ride and then the other one seem mixed use and was the one I took out in the rain. I'm now putting together an old mountain bike as a winter ride. It's purpose is to be sacrificed (if need be) to the salt and sand gods this winter. Oh and I'm seriously considering another nice MB for off road use this spring. You can never have too many bikes.