Q:
Do better salvage kits give more material?
No, they tend to give better materials. Instead of 2 Rawhide leather, you’d get 2 Thin leather.
Plus the chance for rare materials and runes/sigils.
Not that I’ve ever noticed. Better grade kits do, however, increase the chance to yield a higher (+1) tier material (though that’s not always desirable), and better chance to salvage upgrades.