Iron Sky said:
I guess for me the issue is what intelligent opponent will actually use castles when you're in a world where the possibility of 50 mages showing up exists? The simulationist in my sees spells like teleport and dimension door and speak with dead and says "these would utterly re-shape society - why is everyone still living in a medieval paradigm?" It also trembles at the thought of looking at 500 spells and figuring out how each would undermine/reshape any rational world in which they exist.
If you look in the DMG at their default city-generation toolset, every major city will usually have at least one person capable of utterly destroying that city or another like it every day, in addition to several dozen casters with access to mid-to-high-level spells.
My simulationist brain, especially when seeing PC casters wield such powers says "why in the past 300 years this city was supposed to be here, didn't some chaotic mage with a grudge flatten the place?"
My default response is to kinda wave my hand and ignore the issue as long as possible, until players start to get to higher levels and they start asking, "if the big bad guy is a level 17 wizard, why didn't he just divine where we were, teleport without error to us and OMGWTFBBQ us when we reached a high enough level to be a threat? That's what I'd do if I was him..."
At the most, it's going to take a day out of his agenda and probably not even that. How many 17th level wizards use up even a significant fraction of their spells every day?
Ok, this isn't going off on a rant, so I'll just sum up: if I have to someone rationalize full-healing after a good night's sleep, it's worth it if it can stabalize the radical caster-power issues I always have with my DnD worlds.
The first step, of course, is to toss the DMG demographic and weath-by-level tables into the same pile of rules that bag-o-rats and conscious-but-dead characters. Then, you pick your named character point, your heroic ratio, and your power curve. For me, it's usually about level 6 for the named character, 1/100 for the heroic ratio, and 1/10 power curve. What that means for my worlds is that for every hero, there are about 99 nonheroic characters in the population, and for every hero of level n (up to n=6), there are ten times as many heroes of level n-1. So, a population of ten thousand should, all things being equal, support 1 3rd-level character, 10 second-level heroes, and 100 1st-level heroes. Soceities that are willing (or forced) to put large segments of their populations through potentially-fatal upbringings can up the heroic percentage, as can heroes working specifically to train others on an individual level. What all this means is that I now know what kind of population I should need to get a strike force of 4 level 5 rangers, should I need one. In addition, it tells me that effects of characters up to 6th level are theoretically purchasable; Continual Flame is for sale, Raise Dead is not. This gives you a nice level of additional crunch, with built-in guidelines for how often its encountered (Sleep often, Acid Arrow sometimes, Fireball rarely).
Past the named level (and its accordant CR), nothing is generic. If I choose to drop a Wizard9 into the campaign world, it is as a distinct individual, with a name, personality, bits of backstory, and plan for how that character would affect the surrounding world (or lampshades firmly hung explaining why he hasn't.) I also tend to make outsiders unique and named; IMC, the Dark Eight are the only eight pit fiends in existence, and there is only one solar. (I also hack Planar Binding / Ally into something slightly less horrible, as well. They now always cost XP; bringing Outsiders to the Prime is always a big deal.)
Plus, there are a lot of dead things in my campaign worlds; it got to the point where one player complained that he was afraid to start liking any of the small towns and farming communities the party encountered on their travels, because there was a good chance that one of them would have been raided by something nasty before their return trip. And, to your other point, after the PCs see what a high-level named character can make of a large, industrious, well-defended population center, they endeavor really, really hard to remain off of his radar.