Ultimately it comes down to this:
Clerics should be the best healing option for groups, currently they are not.
1) Heavy damage on single tank - this generally is either a stoneskin solution or regenerate solution. Regen and stoneskin can be cast Fair-Perfect, heal has to wait until Bad/V bad - so you will always get a stoneskin or regen before a heal.
2) Group damage - Ameliorate is nice but healing wave and healing cloud seem superior. And obviously as everyone has pointed out, healing mist is a complete joke.
Additionally, there's buffing/debuffing, but as Reed notes, is anyone really memming holy auras or prayers? It's basically cloak of bravery and that's it.
Cure blind is fine, as is legend free action.
But just off the top of my head, some other options are:
1) Make healing mist superior healing to healing cloud and healing wave, potentially adding the ability to remove some negative debuffs, for instance, would be really useful for high priest in istar, etc.
2) Create a heal over time that is better than regen and healing cloud for clerics so it makes sense for clerics to cast before shamans or druids, maybe keep it divine so you can choose between that and heals or something. Perhaps even a mix of steelskin and regen or something.
Bottom line is this - the reason people don't play clerics is because if there's a shaman or a druid in the group, they pretty much have zero to do except maybe toss a heal or two at end of zone. I used to joke about being so excited to cast a heal or 2 last wipe during a zone, but it was true, I was basically afk and just around as an insurance policy which is boring as hell and obviously not what is intended from primary healing class.
Personally I would nerf shaman and druid heals, cut regen and healing cloud heal hps in half. But I'm a dick and I'm sure the rabble would revolt, so maybe keep the arctic inflation going and buff up cleric healing so the are the PRIMARY option for healing. And they cast first - with regards to buffing party, but especially for healing high single damage or high area damage.
Otherwise nobody will play them past early wipe except for a few people.