[dogscoff]

Still, building cities should be considered something like a personal goal or a show of power.

If you're talking purely in terms of mineral production, then yes, but you forget all the other advantages a city facility can provide:
Resource storage
Shield generation
Unit storage
Research, intel, org and rad production
Space port and resupply (in some cities).

These are not to be discounted, especially on those planets or systems where you only have one or two facility slots and you want to cram as much as possible into a limited space. In my single player proportions games the vast majority of my facilities are cities of one kind or another.