CarrionCrow: I wouldn't mind the game book add-ons if they were in a more coherent mass, if that makes sense. They're very scattershot, content-wise. If it was something like core rulebooks plus technical readouts (the books that contain all the different mech designs), then I'd be sorely tempted.
ElTerprise: Yes. I know what you mean. That would be better indeed. Nonetheless it's okay that they offer them - there are sure people who like to get them regardless (although i find them quite pricey)....
They're useful, but it's very scattered. What you need to start are the two main rulebooks (which used to be one rulebook, but anyway), the readouts to check out and pick designs from, and the miniatures and maps to actually play the game.
Everything after that is an add-on. Nice, but very optional.
Also, said screw it. I'm now a backer on the same level as you. =)
(I sincerely hope you're in the mood for PVP Battletech when the beta starts. You'll be the first person I bug to fight against. >=) )