I think 8-9k can be fine depending on your setup. It's going to depend on how much spot healing you have to do, which depends on how/what the other healers play. In general, your AoE healing will be better the lower your spirit is as much of it comes from Efflorescence and Wild Growth which scale with mastery but not with additional mana.
If your item level is above 520ish and you have the legendary meta, you're not going to need all the spirit you get on gear. In the current tier it's something to reforge away from, not into.