Each stat affects our heals in a different manner. Intellect is our primary stat and generally the strongest stat that we have. The secondary stats, Spirit, Mastery, Haste, and Critical Chance, all have different manner of affecting our heals and are valued different because of it. Spirit has become extremely more important since the MoP patch dropped. I advise gearing towards maximum possible Spirit.
I'm not good at the whole theorycrafting thing, so I'm going to provide numbers from this posts:
100 Mastery Rating: 0.00837 / (1+0.1995) = 0.00698, about 0.7% relative healing increase.
100 Crit Rating: 0.005568 / (1+0.1535) = 0.0048, about 0.48% relative healing increase.
100 Haste Rating: 0.0078 / (1+0.144) = 0.0068, about 0.68% relative hps increase.
100 Spellpower: 100 / (10180 + 9000) = 0.0052, about 0.52% relative healing increase.
These numbers do have one issue with them. They are missing the math for the inclusion of raid buffs, and since Haste adds multiplicatively that likely lowers the value of Haste in this post. If done with full buffs, Haste should be on top for straight throughput.
Haste and Mastery are extremely close here, but the big difference is that Mastery is more mana friendly. Where Haste increases throughput by letting us cast more spells which costs more mana, Mastery adds a "free" bubble to our heals. For this reason, I follow the stats weights:
Based on how mana has been since the MoP patch was introduced, I think that Spirit and mana regen are going to be much bigger concerns than aiming for Intellect. Because of this, my personal stat priorities for MoP are:
Spirit> Intellect> Mastery> Haste> Crit
I think that I should also mention that for straight throughput, the stat priorities will still prioritize Intellect at the top and Haste above all other secondary stats. This is only in cases where you are aiming for max possible burst healing though. In all other situations I would advise sticking with the above stat priority.