Barbara, conventional wisdom is to leave sharpning until the last stage in the process, but then if you think about it, if (and its a BIG if) the camera manufacturer understands their product, logically they should be able to match their sharpening algorithms to the sensor and (with a fixed lens) the lens more exactly than any third party provider. So I allow Sigma Photo Pro to add a touch of sharpening, i.e. at a setting of -1 (setting are -2 through to +2). Works for me.
Now, I have tried uprezzing DP2M shots using Photo Zoom Pro 4 to 200%, which gives you a file about 168mb (8bit, or twice that for 16bit). In the trials I have so far done, using carefully taken shots, the resulting image, with touch more sharpening added using a low setting in FocalBlade 2.02 did not look obviously uprezzed. I'm not sugesting it was quite as good as a native file that size, but it was pretty close. Not a lot worse than a file from my Hassy H4D-50. I believe there are three reasons for this. First, there is no moire at the limits of resolution, due to the Foveon sensor. Second, the images are exceptionally sharp to begin with, i.e. the native data is very hgh quality and artifact-free. Third, the DP2 seems good at differentiating subtle colours so the images look natural to begin with (if you get the colour temp right).