10 months ago and at level 70 downranking your heals was a standard way to save mana, e.g. by spamming downranked Greater Heal continuously but still staying with almost full mana (because of mana cost and mana regen).
However, this all changed in the patch 3.0.2 (Downranking from WoWWiki) :
With the release of patch 3.0.2, downranking was essentially eliminated for its ability to conserve mana, as all spells are now reliant on current base mana. It can still be used as a choice should a player want to use a faster spell
So if you downrank your heal, you'll be using the same amount of mana but heal a lot less. Generally this is a bad thing (there are exceptions, if downrank is faster to cast but this is pretty rare).
And this is exactly what I did all the way from level 70 to 80, and even *on* the level 80. I downranked all my heals, I was healing about 2/3 of my max heals but I was using the same amount of mana. I did Heroic Culling of Stratholme like this (not easy), I did Spider Wing of Naxxramas like this. Basically using level 70 heals all the way.
For the sake of it? Because I'm crazy? Well, yes, but that's not the case here.
I use combination of addons called Grid and Clique for my heals. Grid is super simple, but modifiable, group/raid frame. And Clique enables you to bind any spell in your spell book to keypress-combinations used with different mouseclicks & cast them on mouseover (so no "targeting" in a sense). All this works beautifully apart from this one small thing...
When you "map" a spell with Clique (e.g. by holding down Alt and right-clicking a spell in spellbook with Clique config open, that spell is mapped to Alt + Right-click), it essentially maps the certain *rank* of that spell. Now you probably see why I was using level 70 heals all the way...
I've been using Clique for a very long time, so of course, I had mapped my level 70 heals to it. In came the expansion, I never went to see Clique's config - why should I, spells were already mapped and I was mostly dps leveling my way up - so all the spells were at level 70 rank.
I'm so happy the fellow priests noticed this when we were doing Naxxramas (don't remember the exacts, but I was throwing 7-8k crit Greater Heals, when it should be closer to 11-14k range). So I remapped all my spells and now it's good.
Conclusion: Addons are very helpful, but don't rely on them to work as you think they work, make sure they do :)
Zemalf out, See You in Northrend!