Have a look at www.thisislondon.co.uk for a few ideas.
I would recommend the package offering the Chicago Musical plus a meal at the nearby Porters Restaurant.
It comes as a deal for £39 and the show itself is worth that.
Other than that I think you packing plenty into such a sort trip.
The hotel is in a great location and there some excellent restaurants and bars close by on the river near the National Theatre.

Oh - and buy an off-peak all day travel card to get around on the tube and buses.
www.tfl.gov.uk will give you a better idea.
Enjoy - it's a great city.