One of the biggest problems with old school D&D (Ron Edwards would probably accuse it of 'incoherence') is that, while it envisions PCs slowly evolving into powerful landowners at higher levels, the truth is that by the time any PC has got to, say, 5th level, he will have so much money that most costs have become trivial and he is able to make huge investments in property and retainers already.
This is not necessarily a problem, of course. But there are ways of limiting the phenomenon - and of making the game world feel richer as a consequence.
As soon as the PCs become property-owners, they should attract burglars. Perhaps very powerful ones. They will, indeed, become a target for fellow adventurers; you can think of their holdings (inn, holdfast, etc.) as being in a sense like an adventure site for NPCs to potentially plunder. YOU CANNOT HAVE A MEANINGFUL CAMPAIGN IF RANDOM BURGLAR TABLES ARE NOT MADE.
I am not an economist. But I do know that inflation is always and everywhere a gold piece phenomenon.
Imagine you have a village of 1000 souls. According to the Rules Cyclopedia, this will generate 10,000gp worth of GDP (though it doesn't use the term) per month.
Now imagine a bunch of adventurers arrive after a raid on a nearby megadungeon, with 20,000gp worth of treasure to spend. They will overnight triple the size of the economy. Should all costs therefore not triple in value? In real life inflation is more complicated. But at the level of principle, this simple back-of-the-envelope approach is sufficient.
How do the PCs find buyers for non-cash items? Some random pieces of jewellery will cost tens of thousands of gp. Is it likely that our 1000 soul village will have anybody willing or able to buy such an item? The sale of big ticket treasure items should really be an adventure in itself - a search for probably very powerful, very secretive, and very eccentric buyers who might try to trick the PCs, or employ them to acquire more.
OK, so the PCs have enough money to hire 500 mercenaries. That's no good to them if there are only 1d6 mercenaries available in town each month, because it's the middle of nowhere. It's very important to establish before the campaign begins what these limitations of scarcity are (how many hirelings are available each month; how much equipment of various kinds is available for purchase each month, etc.), so they exist as a known framework of constraints that you're not introducing just to put the kibosh on the PCs' plans out of spite.
Add your own!