POage counts alone aren't the defining factor of whether a book is worth the cost. I'd argue it isn't that important, actually. Hours of entertainment gained is the best metric IMO. Now, maybe Spelljammer will be a bad value on that front, too. Who knows? But just because it is 30% fewer pages (or whatever, I didn't do the math) doesn't mean you will get 30% fewer table hours or even reading hours out of it. I bought the Ravenloft book, for example, and read it for maybe 4 hours. Then I ran 20 hours of games out of it. Well worth the cost, even if it had been half the length.