One of the things I was disappointed by in late 3e and 4e was the size of the books. 160 pages just felt small for the cost and the amount of content. The size was likely initially related to the number of books being released, but even with the frequency of books shrinking the size of books has not increased.
I don't think so. I think it has more to do with the cost of producing the material going up, and the relative sales going down. Unfortunately, it's easy to slip into a vicious circle - because of low profit margins you cut size/increase price... but that reduces sales, leading to reduced profit margins... and so, because of low profit margins you cut size/increase price...
Personally, I prefer the Paizo approach of fewer hardcover books but each being a big 250-300 page monster.
I'm inclined to agree.
IMO, the ideal would probably be a
very slimmed down core* (one book of ~250 pages), followed by supplements. These should be few in number per year, but should be large books containing lots of info (on the logic that the people who want more than your core provides probably want a lot more than your core provides).
* The reason for the very slimmed down core is to avoid scaring off new players. I'm strongly reminded of the last time I introduced the game to a bunch of teens. They were quite excited and interested to play... right up until they saw the three (3.0e) Core Rulebooks. "We have to read all of that?" they asked, and I watched their enthusiasm die. It's not an insurmountable barrier - I got them playing, after all - but those near-1,000-page core rules
are a barrier to new players. A slimmed core is better.
But for settings, I would go for the reverse - a relatively massive base setting book, giving as solid an overview of the setting as possible, followed by a range of smaller, relatively more focussed, supplements. The (3e) Eberron line being a pretty good model here.
All IMO, of course.