Though shutter lag time may be shorter on the Nikon D3200, any decent street photographer would leave their camera on, as excellent street shots are one in a million and can't wait for you to turn your camera on.
Addressing your first need (street photography), burst mode on the Sony a37 is at 5.5fps or 7fps at telephoto crop. Nikon D3200 is 4fps. The Sony a37's faster burst rate will help you capture street photos with greater accuracy, along with better phase-detection autofocus accuracy over the Nikon D3200. Also the Sony a37 has sensor shift compensation technology, meaning you can walk or even run with the camera and still take shake-free photos as the sensor compensates for your movement. This compensation works with all lenses that Sony and Konica Minolta offers and allows you to take sharp photos even in sub-par conditions (like dark evening shots) that require longer shutter speeds. The Nikon D3200 provides no vibration compensation in body. It requires the lens to compensate for movements (like walking or running which you do on the street) and not all of Nikon's lenses offer vibration reduction. Only "VR" lenses from Nikon offer compensation for running or walking, and VR lenses are significantly more expensive than regular Nikon lenses that provide no compensation for movement. This restricts the conditions that you will be able to take shake free photographs while on the move.
Sony a37 also wins for landscape photography. The built-in panorama and HD panorama mode offers panoramic shots without the need for an extreme wide-angle lens. Nikon D3200 offers no panoramic stitching and will require expensive software and precise skill in order to create landscape photographs that the Sony a37 offers automatically. Nikon D3200 probably wins by slight margin over Sony a37 for outdoor shots. The higher megapixel count allows better cropping (however not necessarily better image quality). The Nikon D3200 is also known for exceptional color reproduction, which helps when taking pictures of wildlife or plants.
However, the Sony a37's screen tilts, allowing high or low angle shots during bright sunlight. The D3200's screen is fixed, making sunlight an issue as it may cause glare more often than Sony's tilting screen.
