Purpose of salvage items with stats once identified

Is the only purpose of these items to be salvaged by an expert salvage kit to get the stat off of it for use in another item?

You get runes or insignias from salvaging them, which you can then put on your own armor. You can also just salvage them for raw materials which are commonly used for making armor.

You also have the possibility of getting Rare Crafting Materials from items when using an expert or superior salvage kit.

I was gone for ~6 months and when I came back I seem to be getting more rare crafting materials than I once did. It's actually a pleasent surprise.

I don't believe any rare mats have been added since EOTN, although I could be mistaken. However, having been deeply involved in this game since then, I'm rather sure.

That is correct. No modifiers drop without requiring to be salvaged from another item.

This is true for runes, insignia and weapon modifiers.

Is there a table or something, somewhere, that shows what modifiers are worth salvaging? I have been currently only using ESK for items marked as highly salvageable and then selling the rest for cash.

That's what I thought since I couldn't wear the items, thanks.

Disappointed me when I started. First time a pair of Giant's Boots dropped for me, I wanted to WEAR the buggers

Items with a Rune or Insignia - Identify if you want to use that item on one of your characters or heroes, if so salvage and use it. If not then check with the Rune Trader to see the price of the runes as some you'd be better off salvaging and selling to the trader rather than giving it direct to the Merchant. Over time you'll learn which runes/insignia are worth something.

Weapon Modifiers - Again, if you need to use them on a weapon then salvage, rarely are 'non perfect' modifiers worth anything, but some (such as 19% enchanting) can be worth more than selling to the Merchant.
There is no in-game trader of Weapon Modifiers so any selling will have to be done to other players.

Materials - You can look up the item you want to salvage on the Wiki, this will then tell you what material it can salvage in to so you can decide whether to salvage it or sell it. If you have the time to save up stacks of materials then these can be worth a lot more than selling the un-salvaged items, check the Material Trader for prices.
Also consider any armour you may want to craft in the future and what materials it requires so you can stock up on it while you play through the game.

'Highly Salvageable' items will just yeild more of the material or a better chance of a rare material, you can still salvage any other items to also get materials from them.