There are currently only 4 options for city specialization - they aren't too bad to be honest.
It's just, there are many settlements that don't particularly fall under the specializations of gildar, tech, or arcane... and which might not really need a mire skarth (or bandits... eh???). There are plenty of possible specializations that can be awarded to growing settlements.
When a city levels up, I think it'd be nice to display a city level up menu - it should display what resource levels the city produces, what harvested resources are linked to the city, the buildings in the city, and most importantly, what specializations it has previously undertaken.
Some new specialization options might include (in the current 20% - 30% - 40% etc. theme)
Agriculture - settlement produces more food
Commerce - Settlement gains 1 additional caravan per specialization and/or gains additional income from trade caravans
Tourism - Settlement produces increased diplomatic capital and/or units regain health and essence at increased rates while resting in settlement
Industrious - settlement produces increased harvested resources. Does NOT include gildar, food, horses, wargs, or diplomatic capital.
Bastion - defending units gain increased defense
Bureaucracy - settlement's maintenance costs are reduced
Military - settlement trains units more quickly and/or have more HP - does not include spiders/darklings/etc.
Standards of Living - settlement gains in prestige (+1 each specialization)
Naturalists - Settlement produces more horses/wargs and trains spiders/darklings/etc. more cheaply/quickly.
Efficient Engineering - Buildings are produced more quickly
Patrols/Rangers - roads and resources within the settlements sphere of influence are protected from Faction Creatures and Whatever of level 1/2/3/4 ; does not include rival factions, except final tier protects against rival pioneers (but not any other rival faction units).
May have more as I play/remember.