When contemplating upgrading a piece of armour always keep in mind that the only thing you are going to improve is the defense rating.
Thus you need to ask yourself: Is the defense really important enough to warrant the runes spent and the increased item requirements? Sometimes they are. An upgraded Goldskin makes perfect sense for a mid-level melee character for example. Other times it doesn't such as in the case of a Blizzard sorceress nuking the beasties from afar.
There are, of course a few exeptions. Normal belts can for example often get more slots by upgrading them to exceptional and in a rare case you can even get more block-chance when upgrading a shield (defender->heater) comes to mind. Upgrading boots or shields for an assassin/paladin is also an exception though it would be better to think of the boots or shield as a kind of weapon in that case.
In case of your sorceress I would say that upgrading doesn't make sense, unless you are a type of sorceress who spends most of her time within hitting range of her adversaries (such as a Charged Boltress for example).
Remember though that the requirements change for the item and an additional level requirement penalty is added as a hidden affix.
It's +5 rlvl for normal -> exceptional and +7 rlvl for exceptional -> elite, and +12 rlvl for normal -> elite.
Some normal items (uniques) have properties that other uniques don't for instance; goldwrap (high MF for a belt), venom ward (nice +max resist and reduced duration together on one item), etc (I could go on but I think you get my point).
If goldskin has a property that make it special to you then by all means upgrade it, however some items just are not worth the runes to upgrade, its all what you value.