The main strength of Word of Glory is its cost. No matter how strained mana might get, you're always going to have ample usage of an instant, free heal.
It's difficult to offer talents that mod the other heals. If you have a talent that makes Flash of Light more cost effective or Divine Light faster, then those aren't really filling those niches anymore. We had a lot of problems like this in the past where a combination of talents, glyphs or set bonuses made Flash of Light or Holy Light the obvious heal for paladins, and the other one just died. We want to use all 3 of the cast-time healing spells in Cataclysm, but we're offering the most gameplay around Holy Shock and Word of Glory, because those are what make Holy paladins feel the most different from other healers.
As others have pointed out, Beacon just can't stay as "I heal at 200% effectiveness" in the Cataclysm healing model. It will still give you extra healing, particularly with the Tower of Radiance component.
We're not worried about the AE healing situation. In Lich King there were situations, especially in raids, where healers were called upon to instantly heal multiple targets at once or someone was going to die. With the larger health pools in Cataclysm, those situations are just going to be very rare. AE damage, and sometimes raid-wide AE auras, will still exist, but your tools are more than adequate to handle them. No, Light of Dawn may not take 5+ targets from 50% damage to 0% damage, but it also doesn't need to. You'll have time to top them off with single target heals, or just wait until the next AE heal is available. We just don't think spammable AE heals are that fun. If we wanted them to be a big part of the game, we'd need to make actual AE healing rotations that did more. The LK scenarios of hitting Wild Growth and Circle of Healing on cooldown are not something we want to go back to (plus, we've increased those cooldowns).
We just don't believe the healing situation and the AE healing situation in particular is as dire as many of you are suggesting. We balance the encounters around the class capabilities, so if many groups are struggling on certain ones, those will be adjusted accordingly. We generally don't give classes new abilities because they have trouble on certain fights. If you're finding that you are just constantly behind the curve on every encounter, even the trash, then you are probably doing something wrong (attempting these dungeons undergeared is something we are seeing a lot) or your class has some kind of systemic bug that is affecting all of the healing you do.
Overall, the dungeons probably will end up more challenging than they were in Lich King. Even if we eventually end up with 10 minute chain pulling 5-player dungeons in Deathwing gear, there is no need to start out that way.
We're being asked to deal with a total change in healing philosophy and approach, but the model is broken in a way that seriously disadvantages us at the same time. The devs say that they're not focusing on numbers - fine, but don't expect any useful feedback until you have focused on numbers
We get plenty of useful feedback in the current environment despite occasionally borked numbers. If you find it's not fun for you until all of the numbers are in place , then my advice would be to put aside the beta and wait until the game is live.