So, I have the Tom Baker VHS reconstruction, and the Paul McGann/Lalla Ward Audio Play version. Is there anything different/extra in the Lalla Ward reading the Book version that would convince me to buy it, when I already ahve the other two versions, which I love?
The reconstruction was only part of the story, as you know. The McGann version was a reimagining/retelling which was adapted and changed considerably to allow for the Eighth Doctor. Roberts's novel is a 300+-page expansion of Adams' original story. I think it's a no-brainer, personally, whether you choose the (unabridged, I believe) reading by Ward, or the book itself. This is the whole enchilada as opposed to a taster plate in terms of the Baker reconstruction and a whole different recipe in terms of the McGann version.
Also, this is the first "new" Fourth Doctor novel to be published in about 7 or 8 years and marks a return to publishing novels in general based on pre-revival Doctors which BBC Books had retired back in 2005. That's a major selling feature in and of itself.