It could be. One problem with Mastery is, if the shield is not consumed, then it's worthless. (Then again, if we crit a heal on a target who doesn't need it, that's worthless too, so this is a pretty poor argument against using Mastery.) Another problem is, if the shield is not consumed, and you throw another heal on, the new shield amount is not added to the old shield amount. However, smaller shield amounts do not overwrite larger shield amounts, so it does at least benefit us in that way. In theory, you can Lay on Hands the tank after a battle, then use Holy Shock to keep the big shield rolling until it's needed.
Part of the problem with judging stats at his point, is the problem of stat decay. Once you hit 85, you need a ridiculous amount of any rating in order to make great gains in that stat. If we were able to stack 30% crit, 30% haste, or 30% mastery, for example, then we could do a complete analysis of each stat, and give a solid yea or nay for each one.
Another problem is that of talents. For example, sufficient crit to maintain 100% uptime on Conviction is desirable, but crit is otherwise a generally lackluster throughput stat (1% crit is 0.5% throughput.)
Yet another problem is the disparity between our secondary stats. Crit is a throughput stat, as is haste, but mastery acts somewhat as a throughput and mana conservation stat, while spirit is almost entirely a regen stat (Enlightened Judgements allows it to act as a throughput stat, indirectly.) It's obvious that one is most likely going to act as our "Best" throughput stat, but individual cases may make a pure regen stat like spirit a more desirable choice than any of the throughput stats. This problem has not been a serious consideration in the past.
Finally, there is the issue of gear consolidarity. The biggest problem we saw in WotLK was the wide variety of gear available. It was very rare to find two Holy paladins wearing the exact same gear, simply because we had so many pieces to choose from. At the current time in Cataclysm, there is a very limited gearset available. This is partially due to having a solid reason to stick with plate in almost every instance. At its core, I believe that Reforging is Blizzards attempt to tame gear inflation while not leaving the players screaming "OMG THERE'S NO GEAR ANYMORE."