Depends on what gear you have, but I had a lot of spirit + crit stuff, and I gemmed full crit in yellow socket, spi+crit or int+crit in blue/red sockets and spirit jewelcrafter gems. I was ~24% crit (that's ~30% raid buffed), ~10k spirit, ~3k haste at ilvl 510 (I don't remember exactly, but that's the general idea)
Now I finally got enough gear (at 522 ilvl) to get safely to the 7.6k haste breakpoint and it felt great (like I-can-do-as-much-healing-as-the-holy-paladin-and-disc-priest-instead-of-being-30%-behind great, plus healing with more haste is more fun). I still have 8.6k spirit (10k with spirit flask) and ~25% crit raid buffed. I only did a farm raid for now but it seems like this give me enough mana to sustain the haste.
Concerning the spirit for Mana Tide : I only normal 10-man, but I suppose you too if you're ilvl 510. If not, this may not apply to you. What I noticed is that if you're 3-healing normal raids, then your co-healers shouldn't need your mana tide that much if they don't excessively reforge out of spirit themselves. If you're 2-healing the fight, then your own throughput is important because you can't rely on your co-healer all the time, and thus you should only take enough spirit to sustain your own needs so that you can heal enough when the other healer can't heal. Also Mana Tide still give your co-healers mana when you have less spirit, just (a bit) less.
Of course in 25-man it's different because more healers benefit from your Mana Tide, and you're never the only one responsible for keeping the raid alive (which can happen while 2-healing 10-man)