If I create a world with the 'amplified' terrain setting, is ore generation affected? Will ores spawn higher than normal, or will I still have to find them at the same levels? Is their distribution changed? I'm guessing there will be an effect due to the lack of stone to generate in, but it would be good to see some data.
I have collected data using a program called MCAMap, and can conclude that no, ore generation code is completely unchanged in an amplified world.
To check this, I generated an amplified world and quit. Then I used the "Search for Block ID" function, to see the coordinates of every diamond ore that had spawned in the world. The output for MCAMap is, unfortunately, not pretty, but this is what the search found (sorted by Y coordinate).
The greatest Y-coordinate for this sample was 15, which is consistent with the wiki's information on ore spawning, which states that diamond ore spawns below level 16. I am getting consistent data for all other ores. Therefore, I can conclude that the amplified terrain generation setting does not have any impact on the ore spawning code.