Is it better to get a backup bike that's about as good as the primary bike, or do you want a junker?

If you have two bikes that are similar, when one needs fixing you'll ride the other one. Until they both need work, and you just got home from a road trip at 9:00 Sunday night and need a bike to ride in the morning. (Been there, done that!)

If the backup is too bad, you'll never want to ride it, and work on the "broke" bike until 11:30 Wednesday night so you can ride it the next morning.