The karting place is definately closed. The terminal at Kai Tak is in the process of being pulled down.
As for suggestions, you could go up to the peak (on a nice day!
) and go for the short hour walk they have around the peak and take the Peak tram (although it is due for some maintenance this month I think).
Go and have a wander around Stanley market, and have a beer in one of the restaurants/pubs that overlook the sea.