I tried the PDFPrint example of the PDFNetSDK and played with different dpi resolutions and quality settings. While I noticed significant impact on the spool file size, I did not notice any quality impact on the printing process itself. I would have expected that when printing with e.g. 720 or 1440 dpi, the printing itself should take longer than with 100 dpi. At least when using the normal printing dialog in Windows it has significant impact on the printing speed.
Am I missing a printer specific setting?
Most PDF contain vector info (e.g. text and paths). PDFNet preserves this info and sends it in vector form to the printer which should render the content at max resolution.
As a result you should not see a big difference in spool file size when adjusting the DPI. The parameter will play more important role if you are printing huge images.