[MetroMPG]

Do you live in a house or apartment? I would start with adding a coolant heater, even if you're still planning to add a turbo. Your wife has the kind of usage (short trips) that will benefit most from pre-heating the engine. (The reason I asked house/apartment is whether you have the ability to plug in.)

Can't offer any turbo advice - I'm not even up on the theory of turbocharging vs. efficiency beyond my limited understanding that turbocharging's efficiency gains mostly come from downsizing the engine so that peak power demands are provided by the turbo, while light/moderate loads are handled off-boost by the otherwise smaller engine. (Similar to the approach of hybridization.)

Will be watching with interest.