As much as I love to play games with 500 - 600 page rulebooks, I think it's too many rules unless the game is a toolkit. HERO is perfectly justified in having that many pages and more for a rulebook because of what it is, while at times, I find Pathfinder a bit redundant in spots (but I love PF!).
I really would like the next version of D&D to be scaled down so that the "core" ruleset is at most 128 pages for a PH. For the DMG, if necessary, another 128 pages. Even when I think about this, I'd still like to see it whittled down to 64 pages for a PH and 96 pages for a DMG.
Or maybe 64 pages for the core and 300+ pages for the optional modules to emulate the various editions. I don't know, I'm just tossing out ideas here.
The more rules support an activity has, and the less it relies on DM fiat, the more comfortable I am with it being "important", as DM and as player.
The big problem I have with "creative and non-violent" solutions in DnD is they tend to make the really weak non-combat rules more important than the well-crafted and coherent combat rules. Game rules are the physics of the world, and good ones do more to create immersion, for me, than anything else. DM fiat is inherently a break with those rules, and thus risks breaking immersion.
I think that rules should cover most things (about 75%), but I can't see them covering every conceivable situation. As new things come up, the group discusses new house rules to address them.