I am all for n+1 but having two of the exact same bikes is a bit silly. Having multiple bikes that are different enough is handy. I mean certainly a lot of bikes share some common parts because they are good parts but I try not to make all my bikes the exact same. Variety is the spice of life and give me plenty of spice. That being said you could have a backup laying about but I would probably instead have some nicer parts for the current bike and plenty of spare wear items so you can get it up and running. I would still have another bike or two or three or four or many more but if you have one main bike that you love get parts to keep it running and save the other parts for winter or when you have an issue and replace it.