I would love the option to generate a large city butted up against a mountain range. 

To be honest I don't see how a mountain range would affect a city. A city needs to be really large (like a modern metropolis) to be "distorted" by such big landscape features as mountain ranges.

Aesthetic appeal I suppose, I agree it would look pretty great but it's all you.

It would be great to have some height features, mountains, hills and cliffs. For how mountains effect village and town planning, see Japanese inland (eq. Gifu prefecture) or smaller towns in Switzerland, but it is mostly that buildings are in long but narrow streaks at bottom of a valley, then few farms where there are flatter areas, usually also at valley bottom. These height features could also be used for water and road generation, so roads going uphill will have serpentine bends and water flows downhill or at bottom of a valley, having more bends on flatter areas.