Image quality is very important – it is best to have as much detail as possible in infrared images. Typically, digital SLRs produce images of a higher quality due to the fact that their sensors are larger than those of point and shoot cameras and with the larger sensors come the better electronics like the signal amplifier and analog to digital converter (ADC). It is also possible to have much more control over variables like aperture, shutter speed and ISO, which all directly affect the image quality, well, maybe not so much image quality as control over how you want your image to look.
However, nowadays point and shoot cameras are beginning to produce images of a higher quality – bridge cameras are available (such as the Panasonic GF-1) which have slightly larger sensors than point and shoot cameras, detachable (smaller) lenses and more control over variables such as aperture, shutter speed and ISO. Some even allow image capture as RAW files.