This topic has been discussed at great length (there is a currently active thread) on the WotC forums.
Keterys is right, if something has value (and residuum certainly does) then it WILL have some exchange for other things of value. That's just part of the logic of value itself and you can't really get rid of it. Its quite true residuum might not be a very useful currency any more than gold is in modern society, but somewhere someone will buy it or sell it for the right price. That price establishes the gold <=> magic conversion ratio. You can set that at anything you want, but what's the point of making it different from RAW?
The "high level PCs can buy a village" issue is THE issue. One good solution is simply to make such things non-fungible. In other words in theory you might be able to assign a GP value to a village, castle, etc. but in a feudal type society these items simply cannot be purchased. The village is part of feud granted by a king or higher level lord. He doesn't grant those things to anyone he doesn't want to and his criteria aren't really monetary. He can't take them away from their current "owners" and those owners won't sell because their social status is dependent on occupation of the land plus they don't have the right to do so without permission.
Now, that doesn't mean its IMPOSSIBLE to buy and sell any kind of property, but having a quantity of money (gold) is not the one and only necessity. It might be possible to drop a bunch of coin in the lap of a lord to have him somehow get you title to something, but there will be a lot more to it than that, like having a patent of nobility at the very least or being of such service to the lord that he might grant one (and note that kings normally are the only ones who can do so).
In other words, its not necessary to split magic from other stuff in order to solve the underlying issue and any way you do that is simply a DM fiat that contravenes logic.