Measured on a one-minute single-boss fight, each 1 % of spell crit adds as much healing as 11.3 points of healing power, and each 1 % of casting speed as much as 28.5. Intellect comes to 2.87 a point and MP5 to 2.65. The weights come from nudging one stat at a time on the benchmark set, so they tell you what your next few points are worth from this gear.
Per point
- Intellect2.87
- Mana per 5 s2.65
- Healing power1.00
Per 1 %
- Casting speed28.5
- Spell crit11.3
Healing power
Healing power is the yardstick the other weights are counted in. Each point adds 85.7 % of itself to a Healing Wave, 71.4 % to each Chain Heal target before the jumps halve it, and 21.4 % plus five ticks of 10 % to a Riptide. Healing Way and Purification then add 35 % to the whole Healing Wave.
Crit
A critical heal lands for 150 %. 
Thundering Strikes and 
Tidal Mastery add 10 % to your heals on top of the 13.0 % on your character sheet.
The one-minute builds keep no Water Shield, so here a crit is healing only, and casting speed leads instead.
Intellect, MP5 and Spirit
Intellect is 15 mana a point, raised 10 % by 
Ancestral Knowledge and 10 % by Blessing of Kings, plus 1 % crit for every 59 points.
For the single-target build it outweighs MP5 on three minutes: 1.67 against 1.51.
MP5 keeps flowing in full while you cast. Spirit gives back 15 mana every 2 seconds, plus one for every 5 points of Spirit. While you cast, 
Mindfulness lets half of that through. A point of Spirit is therefore worth about a quarter of a point of MP5: 0.38 on three minutes.
Your mana runs short on every fight length, so Intellect stays above healing power even on one minute, at 2.87.
Casting speed
Casting speed shortens Healing Wave and Chain Heal and the global cooldown. On one minute you cast rank 10 nearly all fight, and 1 % is worth 28.5 healing power, the most of any stat. On longer fights mana ends the casting first, so it falls to 9.42. Little pre-raid gear carries it. Your sources are the Minor Haste glove enchant, Troll Berserking and the Windshaper's 1 % Wind Blessed.
On every fight
Gear for the length you raid. On two and three minutes crit leads. On one minute casting speed does. On every length Intellect weighs more than a point of healing power, because the bar only just lasts.