Adding exterior basement insulation

[Daox]

I've been thinking about adding basement insulation since I've been monitoring my basement temperature for the dryer heat recovery system. I've noticed it sways a lot more than I'd like to see. In the morning this winter it starts off in the high 40s, and during the day usually gets up to the very low 50s. While this is probably good for the freezer down there, its not so great for the furnace or the water heater, and it also makes for very cold floors! So, I've been thinking of insulating the basement. Since it is already quite small, I think I would like to insulate the exterior. Yeah, this would involve digging all around the house and putting in rigid foam board. However, doing it on the outside will allow me to fix any drainage problems that will show up this spring. It would also cover up the exposed field stone that is above ground, but below the siding. I'd really like some input and ideas to get me thinking more about this.