What good would nuking civilian population centres actually do either side?

The idea that nuking population centres is an effective tactic is based on the frankly naive idea that governments give a shit about their common people, in fact all the evidence strongly suggests they do not, to put it mildly.

The reality is no country stores nuclear warheads and other vital weapons/equipment in an area likely to be targeted by nukes, ie large population centres.

So it seems logical to me that nuking an enemy that's also a nuclear power does not make it less likely they'll be nuked back, in fact it just makes it certain that you will be.

Governments consider most of their population to be "useless eaters" any way, so are not likely to be particularly bothered about civilians being killed by nukes.