Actually everything has been stated...but well, good try. But I do not see... the point of it. You can only compare legendary items with each other using this formula, and still it isn't concise. It would be really awesome and helpful, if this "effectiveness" thingy would be recalculated(much more detailed, and like agreed up on by the whole community). So that the whole thing can be more...precise. And still a problem is that the amount of certain legendary's in the game is unknown/only can be roughly estimated.
And @Ragnash, ofcourse the rarity is a factor. People don't know how many diamonds we got on earth, but they like them and know they are "rare", which leads to a very high price. I believe same goes for NI Items you see often, not so often etc. (I would even say that people think like "I took me twice the amount of time to farm these crafting goodies, so I want double amount of gold fot them").
And @Ragnash, ofcourse the rarity is a factor. People don't know how many diamonds we got on earth, but they like them and know they are "rare", which leads to a very high price. I believe same goes for NI Items you see often, not so often etc. (I would even say that people think like "I took me twice the amount of time to farm these crafting goodies, so I want double amount of gold fot them").