I'm a big fan of the dwarves and my knee-jerk reaction is to give them many mine-related improvements. That said, Khazad is quite competitive, mechanically speaking, so if we are going to give the dwarves nifty mines of awesomeness, we should probably balance that by weakening something else.
Dwaven Mine - Replaces cottage AND mine
- Connects mineral resources
- same yields as mine
- Upgrades over time
- Second Stage : +1 commerce
- Third Stage : +1 production, +1 commerce, +1 food
- possible fourth stage, not sure
I like this. The Khazad are all about Hammers, Money and Defense while having few, potent cities. So, what if the dwarves got one less food from farms and one less commerce from plantations (we could claim that they're new to the surface and as such, not terribly good at above-ground agriculture) but allowed them to build mines like what Valkrionn has proposed anywhere (not just on hills and metal resources). That seems more balanced.
Another idea is to make the Khazad like the Lanun of the land: make a "
dwarven settlement" improvement which acts like a combination of a mine, cottage AND fort but can not be built within two tiles of another
dwarven settlement.
Stage One (
Dwarven Mine): +2 hammers (like mine), +1 commerce (like cottage), +20% defense
Stage Two (
Dwarven Settlement): +2 hammers, +2 commerce, +30% defense, +1 food
Stage Three (
Dwarven Hall): +3 hammers, +3 commerce, +40% defense, +1 food
Stage Four (
Dwarf Fortress): +3 hammers, +4 commerce, +50% defense, +2 food
*All stages connect mineral resources.
*Offers smaller defensive bonuses to adjacent tiles like castles and the like
*+1 hammer from blasting powder, Arete
*+1 gold from taxation and whatever else boosts town yields
*+1 food with Sanitation
*City Defender and Guerrilla promotions should work at these improvements as though the unit were in a city/on a hill
I like this second option better because a Khazad city surrounded by the spammable mine variant would, over time, become an even bigger powerhouse than it is now. Also, the lands around a Khazad city would be filled with nothing except dwarven mines; it is, in my opinion, a flawed design when one improvement supplants all others. The second option, however, would have three or four highly valuable improvements which the dwarves might actually be willing (and able) to guard during an invasion. Just be sure to make the mature rate slow and you'll have your slow growing, highly defensible, hammer and gold yielding improvement for the dwarves. Huzzah!