If you had a date with a Western girl, and you wanted to take her to a nice, good restaurant (Western or Chinese) with a nice romantic atmosphere, where would you choose?

Most restaurants have private rooms. These are where people can get some privacy for business, or some quiet. They usually have a minimum cover charge (i.e. minimum spend) but the rooms are free. If you add a bottle of wine you can soon hit your cover charge which are not usually high.
OK you need to find a nice restaurant as well, as even the crappy places have rooms.

1942
Green Lake Area - 1921 (year Yunda was founded?). and there's a coupla private villa-type restaurants around green lake also. Do some personal recon - look at the menus (so you can both order from pictures).

For noodles and barely passable Japanese - the glass house restaurant (?) - they also serve the more expensive version of the over the bridge noodles.

Shiping huiguan would be my first choice, it's in an ancient building with amazing courtyard, private rooms, and great food as well.

But maybe I'd go for Makye Ame. The atmosphere there is not exactly intimate, but all women love Tibet...

There will be a new fancy tapas bar called Alei in the Zhengyi lu shopping area, right behind Dairy Queen.

It has a scheduled grand opening on June 22. Very large fish tank, brand new-high end, and only tapas in Kunming. That would impress for sure.