To try to answer the several questions here I will say:
There is a chance to extract an armor piece equipped with a rune with an expert salvage kit.
Rare crafting materials can be extracted with both a regular and expert kit by chance. It is not worth using an expert kit IMHO until more empirical evidence of the added chance benefit is presented.
I printed a list of the salvage materials from each item to avoid wasting salvage kit charges. For example, I play a warrior and a cane always gives me an iron ingot, which I need, but other items can give iron + wood+ whatever.
So, I would use a regular salvage kit on the cane, and sell the other item.
I only use expert kits on blue/purple/gold items after identifying them and discover that they possess a rune or a weapon upgrade.
As a final note, I always use the expert kit in my inventory to extract from the item in my storage in town. I seem to have better luck this way, but the likelihood that it matters is low and I am just being silly.
Cheers
