Basic hydraulics bring you earthmoving equipment, piston-based pressurization, hushing and hydraulic mining for their ores, manned entrance-denial platforms using pressurized air cannonade... The possibilities are endless.
Also natural-gas bottling leads to the possibility of flame exhaust protective measures, and the creation of liquid fuels leads to the ability to produce similar compounds to Greek Fire and flamethrowers.
I imagine a city whose center has a deep underworld of tunnels and reinforced housing. The city also has large pipes that distribute gases through the framework powered by waste byproducts under natural anaerobic decay.
The Dwarves have created the so-called 'dust cannons', producing a high-density rain of particulate that sprays out, expending a parcel of this antimagic ore across casters. Canister shot that sprays the battlefield and weakens casting until they jump into water or somehow wash it off. They also have anti-personnel locations near their gates that can be blown at a moment's notice through closed-valve thermal detonation. Ever see the damage a couple thousand gallons of natural gas vapor filling the streets, then being ignited from afar?
I can.. It filled the sewers and lower-than-level places, sending manholes flying and killing almost 150 people and injuring several hundred. It destroyed a square mile... From a one-day supply of natural gas for section of a metropolitan area.
Hell of a deterrent system. Combine with what they would attract to such an area through the knockers and other creatures that live in those underground places. Molten lead showers, excellent protection.
They have mastered basic mechanics and ship their wares to kings and queens. Throw in investments in clockwork that allow them to make Iron Sentinels (smaller, weaker Iron Golems) that can fight in the flames, and they have even more protection.
Honestly I could see a very focused group of dwarves creating a pretty awesome techno-metropolis in a Mediterranean setting. They would be benevolent to locals in providing them the benefits of their lesser solutions for agriculture, irrigation, etc.... But they keep the goodies for themselves. Anything that we could make without computer technology would be possible with a combination of magic, ingenuity, high Craft, materials, and 300 years

. Imagine 3000...
Slainte,
-Loonook.