Easier to give you an example using your -23 mage weapon. If you have a mage with natural 120 magery and equip the weapon it will reduce your magery to 97 but in exchange you will get 97 in that weapons skill. If you were then to equip jewerly that had +23 in magery skill, then you would be back to 120 magery and 120 weapon skill. Most if not all of the weapons you see going for high prices have low negative skill, no negative faster casting, one handed so you can chug pots, high defense change increase, and hopefully some other mods.
If your in factions, you can get the crystalline ring and orni and that combo would give you the 2/6 casting with +20 to magery, so all you need to do is find a -20 one handed weap with no neg with good mods. It's not that hard using faction items to get 45+ DCI, and you will have the 120 weapon skill and DCI which will help when fighting against dexxors. It's more for the PVP players than those that do PVM since SDI is capped pretty low for PVP and no cap for PVM.
