Harold Mayo said:
SNIP a lot of good thoughts
Sorry to digress so much. Really, what happens in a D&D world in terms of your question depends very much on how common people with spell-casting abilities actually are.
No digression at all. Thats was good post.
For comparison my game is rather high magic.
Anyone with access to time and a spell book can learn arcane spells if they have an INT of 10 or more and a wis of 8+
Anyone willing to live by the vows of a cleric and with a wis of 10+ and an int of 8+ can be a cleric
I also use power components. The end result is a lot of magic.
Since many societys IMC integrate magic into the fabric of daily life. Cities are well lit, food is plentiful and cheap and disease is rare
This means big populations and long lives.
A couple of world altering items from my game
Blast Rod --Use activated disintagrate at will. Cost 132,000 or roughly the outfiting cost of a 12 elite troops with magic weapons. Most civilized areas have 1 or 2 of these used for big mining projects. With one a crew of 20 men or dwarves can cut the Chunnel in 4 months
Food 0 Mat (technically this is called a Caludron of Plenty) most cities have several of these. They cost 30000GP (About the cost of a warband) and will produce enough food to feed thousands of people each day. The food is bland but these devices are used to feed the poor and make up for emegencies
Healing Orb- Use activated casts Cure Disease at will. It takes about 30 seconds to cure someone. These toys are also expensive (30,000k each) but they eliminate serious disease in cities almost completly
Guidance Pendant-- This device casts Guidance at will. It costs about 1000 but will make a person roughly 5% more effective
Healing Gauntlet-- This gadget casts Cure Light wounds at will. Every hospital, and most wealthy people will have one of these. It negates injury and can heal a person at the rate of 5.5 pts per round.
Continual Light-- at 90GP a pop you can be pretty sure every city is well lit. No need to burn the midnite oil. Light is free.
Purfier-- This gadget costs 56000. It casts a quickened purify food and drink. Basically the "quickened" metamagic is there to allow the thing to stay activated. It is expensive and slow but one of these will purify a municipal reservoir, eventually at the rate of about 70,000 gallons a day. Most cities have several of these and it will purify (roughly) enough water for 1000 people each day. Combined with conservation efforts most cities can manage pure drinking water. And if there was a cholera outbreak-- No worries, thats what cure disease is for
Most muncipalities also have Decanters of Endless Water to prevent drought and refill aquifers
There are tons more items like this out there but end result is my world is more like Steven Brust crossed with Robert Howard than J.R.R. Tolkien crossed with Mercedes Lackey