but is that worth more than waiting to get an extra 1st-level spell, +1 to spell DC, and +1 to skill points and some key class skills at 12th instead of 8th level?
Generally speaking, no. It is good to have better AC, attack bonuses, Ref saves, etc. Still your character is a wizard. Your main strength is in your spells. Spell DC and number of spells per day are far much important.
Today, your PC may be using a longbow when she run out of spells. But basically, it will eventually become bad idea to do so. You can buy and create tons of magic items and using those magic items are much better option than shooting an arrow or two.
High level mages do not rely on their AC. You should better protect yourself by other method. Say, flying away from opponent, become invisible, create mirror images, create some miss chance effects (Displacement and such), get immunities (Ironguard), etc.
And Ref save is the least important of 3 saves. You rarely die immediately because of a failed Ref save. But a failed Fort save may kill you instantly. And a failed will save may incapacitate you in some manner, or worse, let your character controlled by your opponents.