Yep, much more useful imo is to have firearms in calibers you are most likely to find while scavenging for "stuff". Which calibers to folks tend to buy in bulk? Oh gee, how about ammo designed by and supplied to the military, I used to buy that stuff by the case, but that was when I allowed myself a lot of more trigger-time than I have time for now. I've still got a case of 9mm ball on the shelf and a lot of .38 Special -- much less in other handgun calibers.

If I had a rifle in.5.56 NATO and another in .308 Win I'd stand a chance of finding ammo to shoot. 5.56 will safely fire its .223 Win counterpart and .308 will safely shoot its 7.62 NATO counterpart. 1:9 twist in the 5.56 and 1:10 twist in the .308 and you should have a fairly accurate set-up across a range of bullet weights.

That's just my opinion, YMMV.