I read the books first (loved them!) and then when I saw the miniseries on t.v., I decided to check it out...
OMG, it was horrible! I only watched a couple of scenes and had to turn it off, it was such a bad interpretation of the book. And you're right about the bad casting. In my mind, the characters were not as old as the actors who were cast to play them. And the women were much prettier than Anjelica Houston!
I think that you are also right that they may have been better off casting "unknown" [good] actors rather than Hollywood stars. I mean, the book was the very antithesis of all of that!