As promised, results from using the Sigma DP2 out in Boston. Pretty happy with the results!
The DP2 didn't give me much grief, and all the shots I took look quite sharp and noise free.
The good stuff about the DP2 seems to be the consistency of colors captured by the sensor. Even when pushing the raws, color detail on illuminated building was able to survive aggressive pushing in post (even if the above photos are not pushed that hard). Also, the lens is quite sharp. The 4.69 mpix sensor is clearly the limiting factor for sharpness.
The bad parts of using the DP2 at night seems to be common grief about Foveon sensors. Bright point lights in the scene become bright starbursts. Which can be cute, but is often a bit distracting, especially in these long exposures.
This is also one of the last times I will do street photography in North End, or Boston in general. Looking to move by the start of next year, hopefully I can find good subjects to shoot in the PNW.