Is it worth using master's salvage kits on loot from low level areas? Will I get rare materials from them, or would it rather be more efficient (profit wise) to use low level kits on low level items?
On any item the high level kits increase the chances of getting rare materials. Having said that if you wanted basic mats you could use a basic salvage kit.
I use basic kits for most stuff, and keep a single high level kit that I use only when I want the rune/ sigil. ATM I don't think the resale value justifies salvage for sale, but maybe I'm not in the high enough areas yet to tell.
Remember if manufacturing stuff to get your craft level up you can salvage stuff you've made and recycle the mats; advance salvage to get jewels/sigils back, then reuse to invent a different item for yet more xp. Can be a cost effective way to make xp.