The less spirit you have, the more skilled you are. Mindlessly stacking spirit is clearly for noobs who can't manage mana. Personally I'm comfortable with 10k spirit unbuffed in heroic 25man.
So what you're saying is that when you raid, you can heal really strong for the first 3-4 minutes of a fight, at which point the other healers in your raid have to carry you for the rest of the fight? I'd be really interested to see how you handle a fight like Elegon or Windlord when the heaviest healing is at the end of the fight, since you obviously don't have any mana left. Don't make sweeping (and frankly arrogant) statements unless you're prepared to qualify them somehow.
OP: it depends on where you are in progression and what your playstyle (and your other healers) are like. If you're learning a fight, I recommend more spirit, since you'll likely be spending mana inefficiently until you get a feel for the damage flow of the fight. The more spirit you have, the easier it is to focus on learning the fight for a few attempts rather than having to watch your mana consumption constantly. If you've gotten to the point where you are comfortable with most fights, intellect can become stronger, since you'll be healing more efficiently and your mana consumption will decrease naturally. The catch is that intellect increases spell power, which should increase healing per mana. But the increased mana efficiency requires you to not waist spellpower on overhealing.