On a one-minute single-boss fight, 1 % spell hit is worth 12.4 points of Spell damage, 1 % crit 11.9 and 1 % casting speed 14.0. Per point, Shadow damage is worth 0.90 and Intellect 0.22. The weights come from the benchmark set, so they price a little more of each stat on top of that gear, not on yours if it differs a lot.
Per point
- Spell damage1.00
- Shadow damage0.90
- Intellect0.22
- Fire damage0.10
Per 1 %
- Casting speed14.0
- Spell hit12.4
- Spell crit11.9
Hit
A level-63 boss resists 17 % of your spells before hit. Hit stops helping at 16 %, because 1 % always misses. 
Suppression gives 5 %, so you want 11 % from gear, and this set has 8.0 % in all. Every spell you cast misses at the same rate, dots and banes included, so hit sits at or near the top of the list on every fight until the cap.
Crit
Crit is worth more to you than its tooltip suggests. 
Ruin at 5/5 makes Destruction spells crit for 200 % instead of 150 %, and on one boss every Shadow Bolt crit puts up 
Improved Shadow Bolt for 12 seconds. This set sits at 17.4 %. A point of crit costs about 60 Intellect, which is why Intellect's own weight is low.
Casting speed
Haste shortens Shadow Bolt and your global cooldown, so it buys more of everything. Pre-raid gear barely has it: the only haste in these sets is the 1 % glove enchant, on the fights where it wins the slot. Its weight swings between fights, from 4.68 on two minutes against three bosses to 14.0 for the Troll on one minute.
Spell damage and the two schools
Shadow damage is worth 0.90 of a spell damage point and Fire damage 0.10. Those two shares are how your damage splits by school, and together they make one spell damage point. So an item with plain spell damage beats one with as much Shadow damage, and Fire-only items are worth little.
Intellect, Spirit and mana
Intellect gives mana and a little crit. Spirit adds a point of mana to every Life Tap, and 
Improved Life Tap, where the build takes it, a fifth more.
On one minute your mana bar, the potion and the rune carry you through without a tap, so Spirit and mana per 5 seconds are worth next to nothing.
On every fight
Hit and crit trade first place by a point or two between fights and factions, and casting speed follows them everywhere but the Troll's one-minute fight. Gear for hit until your spells stop missing at 16 %, then for crit and spell damage.