Correct it will affect your THACO for ranged weapons.

I hear what people are saying about not an important attribute, but when your mage is low on spells I find it useful to have him at the back of the pack lobbing darts, great for disrupting other mages spell casting (better than doing nothing), and what with the amount of magic darts on offer throughout the game if your mage is equipped with Darts of wounding and suchlike and has one of his proficiency slots expended in this field, he can do quite a bit of damage.

However I do agree it is more important to boost the mages intelligence and constitution first and then his dexterity.

http://www.tgeweb.com/ironworks/cgi-...miles/wink.gif

It's also good when you're thwocking someone with Melf's minute meteors (I love that spell) as they're ranged weapons. Or if using one of the boomerang daggers

Yes, the boomerang dagger is a really good weapon that should be used by your mage. If you have THACO bonus to ranged weapons it is good to raise your dexterity.

9 in dexterity is the same as 15 in dexterity when it comes to THACO, if you have 16 you get +1 to THACO, and if you have 17 or 18 you get +2 to THACO with ranged weapons (+3 if you have 19, up to +5 if you have 25). The AC isn't that important for the mage as I said before. I don't think you should change the stats because of this.