Here you're conflating different things.
3E came with the larger numbers expectation built in. The designers did not take it into account because it crept into the system because prices existed. They took it into account because they were supposed to all along!
You can have prices without the expectation.
Take 5E for example. The core three books expect nothing. Nobody can go back in time and magically add in such expectations.
Adding prices to a supplement helps the DM whose players want to spend their gold on stuff but not on downtime things unrelated to the quest at hand. It still does not magically alter the math of the game or its expectations.
No, actually, that's not quite true. You can see, over the publishing life of 3e and then 3.5, a constant upward power creep in modules. To the point where early 3e modules, like Return to the Temple of Elemental Evil, are significantly less powered than later modules, like Savage Tides or other Paizo Dungeon modules.
For example, a later development that you see is the addition of NPC levels onto creatures to bump their effectiveness without changing their listed CR's. This is something you don't see in earlier modules because, at the time of writing 3e, and even 3.5, they hadn't quite realized the impact of fungible magic items on play. How could they really? They hadn't had time to see this effect and the development of things like the Big 6 items.
So, you can compare modules from, say 2000 and then modules from, say 2006 and you'll see an almost straight line increase in DC's and encounter difficulties, despite the modules being for the same level of character. Now, part of that is possibly due to the proliferation of classes, sure, but, it's at least partially because of the magic item economy of 3e. Whispering Cairn, despite being for the same level as, say, Sunless Citadel, is probably a full level higher in difficulty and arguably more. And, as you proceed into higher level adventures, the disparity becomes a LOT more pronounced.
I think you are underplaying the impact that the magic item economy had on 3e. It seriously impacted monster design (later era monsters are significantly more powerful for their CR than earlier ones) and adventure design. AFAIC, the magic item economy in 3e serves as a cautionary tale for how far reaching a seemingly fairly innocuous game element can be.