VALIS: I was just wondering, why the decision was made to go with xp=gp cost. Ease of use? I’m just having trouble seeing where any wizard anywhere ever accumulates enough money or items to craft even a single crappy item.
The reason is precisely for the reason you don’t like it! That is, because it requires a lot of monster parts that way, which makes magic items rare and hard to make.
So, in ACKS, for instance, a suit of +3 plate armor should be be rarer than a keep. Wales has something like one castle every 6-12 miles. ACKS assumes that there might be a keep every 12 miles, but it does not assume that there is one suit of +3 plate armor every 6-12 miles. The local baron has a castle, but only the scions of kings and the commanders of empires wear +3 plate armor.
Likewise, a wand of fireballs with 50 charges is 75,000gp because a wand of fireballs with 50 charges can be used by a 1st level mage to annihilate an army of 5,000 men. Equipping an army of 5,000 men with just leather armor and shields will cost (20+10 x 5,000) = 150,000gp, so the wand is a bargain.
ACKS has implicit assumptions that the game world is functionally similar to the ancient and medieval one, so it is designed to produce worlds that are relatively low on magic. It’s not as magic-light as, e.g., the worlds of Game of Thrones, Middle Earth, or Conan, but it produces far less magical worlds than contemporary 4e/Eberron style fantasy. If you want a game where magic is as prevalent as in 4e or Eberron 3.5e, it will require some house ruling to achieve.