Despite having larger volumes of data to process, the D3200 shoots faster than the D3100. The maximum continuous speed at which you can shoot on the D3100 is 3 frames per second (fps) and this is 1 frame per second slower than the D3200 which shoots at 4fps.
The D3200 also features an newer image processor to deal with the large 6016x4000 pixel files. Instead of adopting the EXPEED 2 image-processing engine the D3100 uses, the D3200 features Nikon's EXPEED 3 image-processing engine that's found in the top-of-the-line D4 and D800. The D3200 also offers a quiet shutter release mode for discreet shooting - a feature the D3100 doesn't offer.