EDIT: Wrote this up as a new post in the Elemental Ideas forum, https://forums.elementalgame.com/384528
Concerning city spam. Many empire building games have some mechanic for corruption or inefficiency. As the empire grows, the penalty grows, so that the more bases you have, or the farther they are from the capitol, the less efficient they are. They also have various technologies (or government types) that reduce the penalty.
Is there any such mechanic in Elemental? The basic idea of Kingdoms vs Empire would be a good starting point - Kingdoms are smaller, and have a heavier efficiency penalty if they grow too large, while for Empires, bigger is better. The Palace seems ideally suited for a Kingdom wide bonus, while smaller structures like the Tax Office could help the city it is built in.
If there is (or could be added) such a Kingdom-wide bonus/penalty system, then it would work to reduce city spam. Without the right structures, research, or spells, a few, well-built cities would be more efficient than many cities.
My thoughts:
Efficiency bonus/penalty - modifies the output of gildars, research, prestige, materials & construction time for each city. (The mechanic for an individual city bonus is in-game, with the Administrator perk that some NPC's have, +10% production, or Royalty for increased prestige)
City based modifier - individual buildings, spells, or certain administrators, that apply a bonus to one city, offsetting the realm-wide penalty. Tax Office for gildars, Town Hall for Prestige, Warehouse for material production or construction time, Granary for food production (which would need a change, to be built in any town.
Realm wide modifier - the Palace leaps to mind, for overall efficiency. Not sure about any others.
Spells - (no clue how spells will work, but I'm looking at this from a Master of Magic basis) Spells could be cast on cities to give a variety of bonuses, either lasting for a set number of turns, or until canceled, for an up-front casting cost, or using shards in some manner.
Research - various research improvements that give a flat bonus. Caravans, for example, could reduce the realm penalty for all gildar, food, iron & material production, as there is now an efficient way to move goods around, stimulating commerce. Other techs could give a flat bonus.
I'm not sure if this type of idea would be welcome, or if it could even be added to the game at this point. I think it could, from looking at a few of the NPC perks. But it would combat the city spam, at least for Kingdoms. Empires should be larger, imo.