Hi,
1. yes it's worth the improvements - upgrade
2. pds issue - long gone
3. variable bit rate (VBR) or video from your camera. - these are the two causes of pixelation on a video.
3-1. VBR - capture (mpeg) can be at a fixed rate or a variable rate - there is an option to make the change. The CPU size of your PC does dictate if the capture as an mpeg/render is at a lower 3000 or at the higher rate 8000 vbr.
3-2. Camera cause - basically you cant improve upon a rubbish low quality capture image on a single CCD with a duff lens. You will get pixelation.
3-3 If you have real concerns you should consider capturing as an DV-AVI from a 3 CCD capable video camera and retain as high a quality video throughout the editing process. Note the higher the spec of your PC really does help in this case.
PD6 is a super Fast-Edit tool and a pleasure to have on a PC or Laptop.
Dafydd