Re: [3.5] Gold.
The fluff is take it or leave it. It seems like an attempt to discourage infinite wealth loops, but then it introduces multiversial potential wealth to allow arbitrary wealth generation until the DM says the cosmos is tapped out.
TG&G/AMT are a bit of a pain for any spellcaster without access to cantrips/orisons (it's kind of weird giving 0 level spells to someone without access to 0 level slots), but mostly serve to give another option for turning one form of fungible wealth into another.
Alchemy, though, is just bad. Not only does it allow you to destroy an enemy's swag with a simple touch attack (changing the target to one unattended item quickly patches that), but it allows for perfectly efficient item exchanges. I get the appeal. But if item X can be exchanged at 100% efficiency and then the money used to buy item Y, that helps T1-ify everyone too much. (The point of T1 is always being able to have the right solution for any problem. Perfectly efficient item exchanges allow you to quickly have just the right item for whatever situation with zero waste/disincentive.)
You also have the question of why item X can be made for (N/2) gold, but still breaks down into N gold. Changing it to only give out half the price of the item should keep the economy intact. The remainder of the item's selling price being an overhead for people who would rather pay a gold premium than invest their own life force into an item.