I agree entirely and have started switching to the IC in HKG.
However, for Plats that do consider staying in the hotel, the rules (as explained to me by a senior manager at the hotel) seem to be:
Book Standard Garden View Room -> Get either Standard Harbour View room or Garden View Suite as upgrade. (Choice is often given.)
Book Standard Harbour View Room -> Get either Deluxe Harbour View room or Garden View Suite as upgrade. (Choice is often given.) Upgrade to Harbour view suite are almost negligible probability.
Book Towers Garden View Room -> Get either Towers Harbour View room or Towers Garden View Suite as upgrade
Book Towers Harbour View Room -> Get either Towers Deluxe Harbour View room or Towers Garden View Suite as upgrade. (Choice is often given.) Upgrade to Towers Harbour view suite almost negligible probability.
The Towers operates as "hotel within a hotel". There is no upgrading from "the normal hotel" to the "Towers", irrespective of the room/suite you may have booked in the normal hotel.
Lounge for Plats booked in the normal hotel: There is a separate "SPG Plat" lounge on the 9th floor. This will serve all day tea/coffee & cookies as well as cocktails and hors d'ouveres in the evenings. Plats get complementary continental breakfast from the lobby restaurant too. If they want to upgrade this to a cooked/hot breakfast, they can do so by paying a supplement. (Room service is not an option for the complementary breakfast.)
Hope this helps someone!