Well, I think some buildings should be more effective in high pop cities, and other buildings should be just as effective in any city (yet all costing maintenance of some kind)
I'm pretty sure most developers should know that using building-based maintenance is a *primary* concept consideration when your using a global system without distance modifiers.
There were simply too many simplifications and corners cut during the "design process" for this particular version of the game.
If buildings are not going to cost anything in the way of maintenance, and can be built in any city, and can't be duplicated in a high level city ... and no form of city-number-based maintenance costs ... then ofc ya might as well spam small-time cities for the basic production.
And the way to counter this??? make resources WAY more effective than any city could possibly be ... oh wait ... they are scattered all over the map. And more of them pop up ... leaving no empty space. Were we trying to prevent city spam? We seem to have just made the game more *boring* and not stopped city spam at all.
Honestly it was more fun when we all tried to make all our cities Level 5s cause it actually *mattered*.
How about make a self-sufficient Giant Super city be a viable strategy (with ur first food resource) ... as well as divide your food among the population (as opposed to housing), and have pop growth in each city be relative to current pop * (logrithmic ratio based on extra food).
So that all cities grow in population based on how *much* extra food their is, but bigger cities do it faster. With housing as a "hard cap" of course.
With a *building maintenance* of gold, you would be able to justify the tendency of all your food going (essentially) to any big city with extra housing. Because those larger cities are *more effective*.
Also, since Pop and Food are directly related (but soldiers and food are not) ... Excess Gold will allow some of your population to be converted to soldiers, and the new *lack of food consumption* will cause your Cities to once again fill up. Therefore, excess gold in any one particular "state of economic existence" can lead directly to an increased Military.
Of course, the more soldiers you employ the less quickly your coffers will fill up, so you'll have to wait longer to outfit new troops, which will lower your income even more so ... making you wait even longer to outfit new troops.
This would lead to a Logarithmic Progression of Faction army sizes related directly to the availability of food. From turn 1 to the end of the game.
*It would also make Larger, more central, cities be able to produce troops much faster* - for instance, an outpost may be able to produce 5 pop/turn for new soldiers, while a Capital may be able to produce 100 pop/turn for new soldiers. (in other words, limited only by Income and Equipment costs).
This would lead to more war-like nations fighting over sources of food ... because population makes more money, money makes troops, and to get all this you need food. Of course, Gold Resources will also be important to such factions, but food will become important as well because of the speed their cities will grow AKA new soldiers ready to train.
If you add to that the ability to throw "unorganized" soldiers into the field with 1 turn of training, at a penalty of combat, you can try to go Barbarian Horde on someone you feel would crush to enough of your numbers.
The only resources you would be losing would be Materials and Gold spent on the equipment, but every time a stack of your died your gold-income would sky-rocket, and by the time your gold re-filled all the extra food created by your massive recruitment would have filled your cities with more willing recruits.
MEANWHILE ... someone that doesn't focus on the "burn and churn" meat-grinder approach to warfare could simply keep small armies w/ big cities, and pour ALL their gold into elite units and well-equipped heroes ... not to mention better buildings that cost more maintenance.
.. in this way Gold Mines would still be Very Important but not ALL important. Food would, in the long run, prove to be much more important for the maintaining of an army.
Prestige could still provide a raw increase to population, being thus more important in the early game. Alternatively, you could have Prestige count as *extra food* for pop-growth purposes to last its importance throughout the entire game. (or some system in the "middle" of the two)
With enough gold and food, each faction would have *Free resources* to actively fight over the important resource sites of Lost Libraries and Arcane Temples.
I believe this model also, somewhat indirectly, supports the model of larger battles w/ more soldiers ... if you consider specialty buildings like Dark Cathedrals or Universities costing as much gold-maintenance as 100 soldiers. (a decision between lots of gold for elite soldiers, or spending that profit on large armies or nice buildings)