Will the book be re-wrtten anytime soon? or is it still worth purchasing?
I don’t know if it will be rewriten… and I don’t know if the engine will be updated or recoded… (I hope so…) but I think is a good inversion… the game kit has a lot of nice things to learn, and is a good way to help the foundation.
It works with the actual versions of blender engine, but the best version to work with the engine is 2.25… at least for several things 
Only my opinion
Yeah definitely purchase the book. It’ll further contribute to the foundation and you’d learn a thing or two from it. It’ll help you get started too as no one so far has written a tutorial that covers that much of the various aspects in the GE.
Umm, I still have it in my shelf. Lol, but I don’t refer to it any longer though, but it does have some things in there that I still don’t know how to do. Guess never had a need for it, but it provides a nice comprehensive tutorial.
As something extra go through Snailrose’s really long tutorial. https://blenderartists.org/forum/viewtopic.php?t=22674&highlight=tutorial
Welcome to the Blender GE family.
Jason Lin