As a caster you will -always- have 1% chance to miss with your spells.
Vs target of your own level: 4% chance to miss. 3% chance to Hit is needed for cap. (pvp) Vs target of your own level +1: 5% chance to miss. 4% chance to Hit is needed for cap. Vs target of your own level +2: 6% chance to miss. 5% chance to Hit is needed for cap. Vs target of your own level +3: 17% chance to miss. 16% chance to Hit is needed for cap. (pve)
Raid Bosses are considered level 63 when calculating hit. Therefore you need 16% Hit in order to be capped on raidbosses. You will gain 6% chance to Hit from talents, so the last 10% must come from gear.
Being Hit-capped can be a hard nut to crack with blue gear. You shouldn't sacrifice too much spell damage in order to reach the cap. Before you are in AQ40, you can easily get away with around 5-6% Hit from items.
Remember that the Hit-cap is only needed for bossfights. As long as you have the talents, you will basically be safe on every trash pull you do. Your polymorphs or Counterspells will not be resisted (or well only 1% of the time) so consider +Hit as a purely dps-stat which has no importance in terms of cc resists etc.
Your primary stat for your damage. As a caster you do not benefit from stats the same way as melee dps do. 20 agility for a warrior is 1% crit. However we need 59.5 intellect to gain the same 1% chance to crit with our spells.
Bottomline is that intellect isn't worthless, but it should be sacrificed in order to increase spelldamage in almost all cases.
Any item without +spelldamage is basically a throw-away item.
Chance to Crit
Chance to Crit is a great stat. For Frost it is just as valuable as Hit, and should be considered of same value in terms of dps.
For Fire, Chance to Crit is slightly more effective than Hit. The more spelldamage you have, the more you will benefit from 1% additional chance to crit. As fire you will do 210% spelldamage on a Critical Hit, and have a chance to replenish the Ignite timer should you also get a Critical hit on consecutive spells, resulting in a massive damage increase when you have multiple crits in a row.
It is a lot of work to figure out the theorycraft behind the +crit vs +hit. And if you're really interested in how to figure that out, then I advise you to download the addon: Theorycraft. But as a horribly-simplified rule of thumb for pre-raid geared mages i'd say:
As frost: 1% Hit = 10 spelldamage 1% Crit = 10 spelldamage
As fire: 1% Hit = 10 spelldamage 1% Crit = 13 spelldamage
So what you want to do when looking at an item is to convert the Crit and Hit into spelldamage and then compare it to another item. Whichever item has the highest amount of total spelldamage, use that one.
Stamina, Intellect, Spirit and Mana/5sec
Stamina is allright, but don't overdo it. In most raiding situations, if you're taking damage it means you're standing at a wrong spot. Whatever stamina that you end up with after prioritizing solely on +spelldamage items, is what you're going to end up with. Don't worry about it. Don't pull aggro and don't stand at a bad spot, and you'll be fine.
Intellect grants 1% chance to crit for every 59.5 intellect, and increases your mana pool with 15 mana per intellect. Seen from a dps-point of view, this is not a very useful stat. Get whatever intellect you can from your best possible +spelldamage items and that will be fine. Compensate with Major Mana Potions if you're going out of mana.
Spirit and Mana/5seconds. Well, these stats are absolute garbage in my oppinion. I'd say that 1 mana/5 seconds is equal to 1 spelldamage. Others may disagree, but fact is that there are just not many fights out there which lasts so long that you end up going out of mana.