The thing about defense on a mage is that you need something to trigger the dci as you said, either wrestling/anat & eval/ mage weapon or a weapon skill (such as fencing/swords/mace/archery) In regards to your 0% wrestling that depends on your race. If you are human you have 20 skill in all skills so you will have defense, although it is so low it is barely noticable. It is the same as occasionally you will parry randomly during a fight, whether with a mage weapon or a shield. You have that low skill in everything so there is always a chance. For pvm i always suggest anat/eval due to slayer books however with the tight templates now you can be ok with books and carry a staff of the magi/ mage weapon of some sort for times when you are running threw some heavy hitting spawn. A mage weapon gives the weilder defensive evasion = to magery. In your case with a staff of magi being a -0 mage weapon, you will have 95 "mace" weapon skill. This works for both triggering defense and triggering offense. Many mages now use there mage weapons (planeswords ;/ ) in between spells for a chance at a hit, this is free damage and helps to interupt casting.
The best example i can think of right now is on the way to navery. There is that hallway packed with spiders, a blood elemental and such. running threw that spawn with a book in your hand you will get pounded on by the monsters. Put a staff of the magi in your hand and you will get hit still, but much less then before, possibly not at all if you have high dci and 120 magery. Then once you get into the navery cave, switch to your spider slayer book and have at it. In a situation such as navery, to have points in a weapon skill/defensive skill would be a waste usually since you can just sit back and cast. In a heavy mob of harder hitting, higher level monsters a mage weapon may prove extremely useful.
defense on a mage has to be considered in a few ways, chiefly regarding pvm. 9 out of 10 pvp mage hate to go into protection to cast. Pvm mages tend to rely heavily upon this spell to cast invis's and such while being hit/ casted on. If this is your case, and you run protection frequently then i wouldnt worry about defense on your mage too much. In a pvp/pk situation u must realize that a mage without a mage weapon, or defense will get hit 100% of the time, where 120 weapon against 120 weapon you will get hit 50% of the time (before dci/hci are factored in)
I still highly suggest a staff of magi in the bag, but protection is a defensive counter some mages prefer, just remember it drops casting speed to 0, lowers your phyical resist and drops resist spells down, so carry some orange petals/cure potions and possibly a trap box.