They dont get worn out sitting around and not getting shot, but that's the whole point too. If you only have "one" of something, and you're the least bit realistic about using it and keeping up with it, then its getting shot a lot.
And if its an older gun you got used, you have no idea as to how it was shot and maintained in the past and how its going to perform going forward. Is something like that worth betting your life on?
This is a NY DOC trade in I got a while back. This one didn't look like it was shot very much, with no wear in the finish on the recoil shield at all, and only very minor finish wear in the usual places you would look, but the second time out with it, the barrel spun off while I was cleaning it. No "pin", and all it had was a big lump of some brown thread locker on the threads.
I cleaned it up, put some blue Loctite on the threads and timed it back up the best I could and have been shooting it ever since. Its the one I shoot all the time in dry fire and at the range.
I have a number of other snubbies too, and randomly shoot them a good bit too, but, as much as I like this one, unless there was no other choice, this isn't one Id carry.
And don't assume that just because you have a bunch of the same or similar "type", the MOA is always the same. If you're mixing S&W and Colt revolvers, etc, that have different things going on in how they work and what you need to do to run them, they are not "the same". And that goes for anything. You see people all the time at the range when their gun stops or does something they weren't expecting, and there they are, just standing there staring at it, and thats with a gun they know. Whats going to happen under stress?
By all means, carry and do what you want, all Im saying is, daily and/or regular mix and match, especially with things you don't know where they stand as far as history goes, and you cant work without having to think about working them, especially under stress, isn't a good thing.