With all due respect, I read Girl with Pearl Earing and found it .. well .. less than inspiring. The writing was "ordinary" and the story seemed forced in order to find things to say.
In fact I found the book so lacking as anything special that I can't help but believe that the only reason possible for its prominence is the fact that it help lend credibility to Hockney's theories which aid and support Modernism in general. The fact that they did not claim that the camera was used meaningfully is really not the point. Whey mention it at all? Vermeer may or many not have used other tools as well which aren't being mentioned.
Is there really credible evidence that he used this device?
Is there credible evidence that any old masters were aided by such devices in the main thrust of their drawing improvements? I think not.
Not saying he used it extensively is a fig leaf to hide behind in order to say that it's not being mentioned to denigrate old master achievements ..... but really it is.
Fred