While I always thought back-up guns were a good idea and a convenience, prior to this year, I used to think you could probably get away without having a back-up Glock G17, G19, or G26 simply because they were so available, extra parts could be had at any gun store or sporting good store, and they were so simple to work on, even if you couldn't do the work yourself, the 20-something behind the counter at the gun store could fix or replace a part on your Glock in 10 minutes or less. However, this year has proven to me even ubiquitos guns like a 9mm Glock are not as always available as they once were, and even accessories can be hard to come by.
I'm not likely to run out in this bad time for buying firearms (low availability and inflated prices) and buy a handful of spares, but the current panic will eventually die down, and when it does, the gun money I've been sitting on since the start of the year, will probably go to buying multiples of some common firearm.