So the devs keep saying that lightwell is a great spell, but they don't understand why people don't use it. I bet if your groups used all the light wells you put down, then you all would love the spell.
To the 4 out of 5 wow players that don't visit forums and just play very casually, they don't even know what the light well does. they see this thing on the floor that looks like a lock's cookie jar but it provides no cookies. after clicking it a couple times and being utterly disappointed (if they ever click it at all), they make a mental note to disregard all future instances of the object.
To the next 15% who know what it does but aren't hardcore theorycrafting players or 25 man raiders, they know they should use it, but when they really need it, they forget its there. Some of these might be used to other healing classes, and expect the healer to do the healing rather than having to go click something to heal themselves. It's like not running instances with a lock for a long time, then when there's one in the party you forget to use the healthstones.
To the 5% hard core players who are running the more difficult content, I imagine they have enough to worry about during a boss encounter that they don't want to keep a note of where the lightwells are. Although of all the players, these are probably the only ones who use the thing anyway.
So why not make the lightwell an AoE HoT centerend around the object instead of a click here type deal? Make it so in order to use the lightwell, players don't have to USE the lightwell. Give it a total heal cap or whatever they need to do to balance it, but as a mechanic, all they have to do is remove the requirement of having the players act on the light well. I think this would make it a much more useful spell.