You could sell your items - And if you ever decide you want them later in the game, remake them. It doesnt hurt.
Since your obviously not using them, there is no point in them taking up inventory space.
Most of the gadgets are easy to make, and if you have any rare schematics you can always make the hard to find items for others.
If your horde, it can be hard to find the mithril mechanical dragonling. You could make those and sell them. Also the schematic for the arcanite one is not necessary hard to buy or find, but expensive. You could sell them pre-made for a hefty chunk of change im sure (if they arent soulbound, i cant remember).
Also you can find the items that are used in quests like thorium tubes. Sell them in lots. Arcanite converters are used in a quest or two.
I have good luck making green lens's and selling them on the AH. People who dont want the make 10 to get the 1 they want are happy to just buy one.
There arent as many items that you can make with engineering that will make you money, but you will almost always have a decent market.