I agree that haste is the obvious way to maximize throughput, but I am highly suspect of your statement:

This smells fishy. Convince me that it's true.

that's indd the most important thing for Ulduar HM's.. i got 234 haste, 26.85% crit and 2664sp(with inner+illusion trinket) selfbuffed atm and noticed that i could use alot more haste.. for exampel on mimiron HM that where still working on i had a couple of times my heals for a Napalm Shell target came a minimum sec to late..

this might also be the result of not having cleared enough who was specificly healing what but still i feel like more haste could save alot of deads or close call situations.. time to farm some badges and get me that new gear from the vendor that is just insane good.. thinking of the shoulders, head, ring and trinket..

Haste vs. crit plays by a lot of the same rules as flash heal vs. gheal debates. Haste is incredibly valuable because it decreases the granularity of your heals. You don't even have to keep up to the damage; another healer will see the tank dropping and assist. Crit has the advantage of giving you more total healing per mana bar, and more healing per cooldown (15% hasted circle of healing's cooldown is still 6 seconds, penance 8).

Haste is more likely to save the tank from a few unlucky avoidance strings since you have control over whether you chain cast and you don't have control over whether you crit. Over the long run, if the tank lives, crit is the mana-saver. You will get your first 6k into the tank (or any spot heal target for that matter) X seconds (.1 sec in my case with my 2 gear sets) before a crit build would.

It really comes down to whether you are running OOM in the fight. If you are not at risk of running OOM in any given progression fight haste is hugely more valuable than crit because OOMing is the most major downside to haste. If you are consistently running out of mana then swap out some haste and load up with crit to get more HPM and HC/SoL procs (which further improve HPM).

Personally I try to to be the hero too much when I get excited/strained, and I pre-heal and pre-hot and pre-shield my mana bar away. I've swapped over from playing a paladin, who until 3.2 had no mana concerns whatsoever. Old habits die hard. Although I'm getting better about canceling obvious overheals and knowing when to go into mana conservation mode and only react to real deficits as opposed to predicted/possible ones.

Haste (at least the last time I checked) was definitely the highest stat for peak hps. It doesn't help with sustained hps.
It's so good because it's quite cheap in fact ;-)

Now, the granularity argument is not huge in my mind. It is really useful only when a boss has capacities that need to be healed in less than about 2 seconds, and can take a player from full life to death in such a time frame. For any other time, reaction times doesn't matter, and hps only matters. I really mean it : if you're loosing players that died in more than 3s, or players that were not full life before the " fatal 3 last seconds", the problem is not reaction time. Either you made a wrong decision and didn't healed in time, or you could have topped them up before (with more hps), and then spellpower would also have been a solution. (In fact, I can imagine a more cases that have haste-oriented solution : basically, those that have let's say a 3s window to heal 2 persons, and where group heals do not work, etc. but they are really similar to the one I exposed).

A few example to make it clear : Kel'Thusad frost tombs are not a problem : an un-hasted flash heal has enough time to save anyone who was topped before the frost tombs. Freya / Mimiron / XT fights can be heal-frantic, but it's more a question of needed hps to keep people alive than reacting in a very tiny window. If you manage to keep everyone a full HP (and therefore have enough hps), then you'll have the time to react and non haste-oriented gear would be enough. The only fight I remember immediatly where you could die because of reaction time was Hyjal's first boss : Rage Winterchill. With undergeared characters (I went there with an alt with around 9k health), the icebolt (the block of ice) could be fatal in less than 2s (4250 - 5750 direct damage, plus a dot at 2500 per second for four seconds). The problem nearly disappeared when you had more than 10k750 health, because you could afford the direct damage + 2 ticks before any healing.