I think this ties well into the whole "buildings do not die fast enough". If your buildings are getting scorched often, then resource management should become an actual issue. If not, then yeah, it's pretty much easy to build forever.
If they get scorched too easily though, it ends up likely being a frustrating thing, with the player unable to keep enough stuff going to use the more interesting things.
With siege units though, to me, buildings seem to fall quite fast. I'm not seeing it as being about the health of the buildings. In my games, if a city gets attacked, under the current health of buildings and power level of siege units, something is going to fall. But.... my playstyle leads to these not being attacked often enough to cause me any real trouble, so I quickly reach the point of resource bloating (at which point everything that isnt diamond stops mattering) and an easy run through the rest of the game, even while using tokens of various sorts. This is with trading active, too, so "excess" resources are being shed regularly. I still end up with WAY too much though. I'd say, I stop paying attention to any of the numbers much right around turn 25-30 or so. This is on Medium OR Hard, which are the two I've been using to test. I'll occaisionally glance at it past that point to make sure nothing loopy is going on with it, but beyond that I tend to ignore it, and with new cities, I just place whichever buildings I havent placed in awhile (or I might just choose at random).
As for the cost increase idea, I hadnt meant increase the cost of EVERYTHING.... just increase the TC costs specifically. It's those central buildings that are the main points; everything else is really just fluff. A city hasnt fallen until that main building is destroyed, and it determines where you can build everything else; having it be easy to construct essentially means the player can just keep farting them out whenever they want. That wouldnt fix the resource bloat as a whole, but I dont see that as that big of a problem, not compared to just having a gazillion buildings in general.
Mick & Misery, do you have a late game save from a recent version I could look at? I'm curious to see how you two are playing.
I dont really have a good one either, as I tend to constantly overwrite the things. I could put one up later though, as I'll probably have a game or two later tonight.
My playstyle overall is generally conservative/defensive, as I usually am with strategy titles. Though, as is the usual for me in any genre, I'm naturally aggressive and a bit prone to random chaos, so if things are getting stale, or if I'm getting (more) impatient, or just for the heck of it, I'll throw out some large effect. Doesnt have to make strategic sense entirely for me to do this. And I wont hesitate to use really major effects to solve problems. I build frequently and my cities mostly consist of resources.
Generally, I have 2 or 3 military buildings per city (and connected schools and such) Anything more than that seems very extraneous. I tend to focus early on on getting the basics down (stone, wood), and then going through the process that I need to do in order to A: get mythologicals available, and B: get diamond and sun/moon production going. All the while producing units and micromanaging where necessary, including throwing out tokens and such. I'll increase the unit count (and thus the military building count) as needed based on woes and whatever is going on. I tend to leave a few spaces open in cities where I can place extra things of that nature. I dont use towers much, because it's bloody annoying to funnel attacking units through there, and siege units tend to be ranged anyway. I put out more barracks and archery than siege buildings. Tend to build more siege only when I think it's actually necessary, or if things are getting dull.
Early game for me tends to be mostly about resource gathering. This changes by mid-game, and at that point I likely have tons and am not really looking at the bar too much (unless something changes the situation, of course). I do alot of micromanaging of battles overall when possible via pretty much every available method, from smiting and "unit up" to crazy token effects.
Dunno how much that helps, but that's the best description of it.