Fifth Element said:
Have you seen the wealth by level guidelines in the DMG? 9th-level wizards ARE rich.
Actually I don't think so. They have about enough to buy one or two moderatly priced items, one true resurrection (most people don't even consider lesser versions an option), and maybe a few weeks worth of spell components for the most costly spells (permanency, etc).
Rant on...
Anyone of level 9 can find themselves broke very quickly unless they have a flow of income. I personally think the wealth by level guidelines is rather silly, and makes little mathematic sense. I believe the "rule" came into the effect because magic items became easily available (as opposed to older versions of the game), with magic item K-Marts and Wallmarts in every city and most towns. But, with this scenario available, the average process of dungeoneering will make a moderately successful character a great deal more than that "wealth table," and doesn't even work out mathmatically.
If magic items were a true rarity (i.e. not easily available for purchase), and crafting took longer (as it was in older versions of the game), magic items are safely in the "it's just not available so it doens't matter how much money you have," catagory, then money becomes used for what it should be: status, land, bribes, research, maintaining equipment and resources (i.e. the furthering of the campaign). The unbalancing effect of wealth becomes curtailed or at best eliminated. Characters won't be focused on saving up for that +3 ring of protection, they'll be saving up for furniture for their mansion, or nicer clothes, and other more realistic, rewarding, and roleplaying focused expenses.
That's why I like the original poster's idea. Should the entrepreneurial character be illogically disregarded, or should he be rewarded for his ingenuity? And...come on...if Walls of Iron or Stone will negatively impact the economy (which you are right, it should given time...alot of time), why doesn't the saturation of magic items from leagues of adventurers over the course of years negatively impact the market (no logical reason it shouldn't). "Sorry, pal. I can only give you 300g for that Helm of Underwater Action. I've got eight and can't sell em." Hehe.
Rant off.