I have the book - it contains a lot of useful information, i use it for reference for suspension/driveline things.
It goes into a lot of detail about the xjs, which would be useless to anyone without an xj.
Also has some writeups about different peoples builds. Reading about someones trail rig with coilovers and 37s is purely entertainment for most.
I say go for it - i dont think the bookw as alot of money. It was a pretty good read.