Chix,
HGVC is just an old tower at the HHV that has been converted to HGVC. I don't know what type of upgrade you might get since the HGVC units are sold as time-shares. For the PIP, most of the participants using award stays got upgraded to suites. Of course, that was before the Kalia Tower was built and opened. The upgrade may be to a suite in the Rainbow or Tapa Tower or just a regular room at the Kalia Tower which has the Executive Lounge.
If you have time, take the HGVC tour while you are at the HHV and you will receive HHonors points.
TF