Update to my earlier post: GM currently has 4300 dealers, so roughly 10 times Mitsubishi's U.S. dealer count.
Source: http://online.wsj.com/article/SB1000...452221502.html
That should help put Spark vs. Mirage sales in perspective.
One thought though: I suspect GM has a significant percentage of dealerships outside of sub/urban areas (think of all those pickup sales), whereas Mitsu is probably exclusively sub/urban. By this theory, Mitsu should be able to show better results selling a city car on a per dealer basis.