Big problem with this is that the airline lounges are in the Departure Level. Once you've entered that level you are expected to leave by plane. You can't get back landside without some drama, which may take a significant amount of time.

You can get the Airport Express with a credit card, but the Star Ferry still needs cash or an Octopus.

The observation wheel is pointless - you only rise about one fifth of the height of the buildings, so it's not like the London Eye, for example, where you get a view over all the surrounding ones.

You can check in before you leave the airport, giving you a few more minutes on your return in you're happy to cut things fine.