You make a few different points here, none of which needed to be made.
You note that mastery is more useful when your target is at lower health. Not only is this obvious from reading the tooltip, I already mentioned it earlier on the same page as your post.
You suggest that since doing the math is hard, we shouldn't bother trying. I don't think you understand what we do here on these forums.
Why would you compare the value of any particular stat, such as mastery, for different classes, with different play styles? This isn't useful at all. As long as all 5 healer specs have the tools to do their jobs, it doesn't matter if mastery, or crit, or haste, or whatever is more valuable for one class than another. It's like you realized that druid tanks don't get much value out of shield block, and had to post about it.
Also, don't start a new line when you start a new sentence, and use proper punctuation.
I see the restoration shaman Mastery bonus, as most of the posters here, the best thing -- or worst thing, depending on the hp% of the target. While Blizzard developers could have given us a flat increase in healing or shielding targets, they decided to give us a dynamic bonus, one that would help in times of need but that would totally fade out if the raid overgears the encounter. Because of this I would not even try to get a "ratio" between Mastery and the benefits of other stats, like crit and haste.
It is impossible to do a math model that could take into consideration the tank damage, all incoming heals and the Personal Decision of the shaman healer. ( impossible = not within the grasp of someone that doesn't work on the math models of the ITER fusion reactor .. ). And since it's not possible to model all the incoming damage, heals and shields on a tank or raid, I don't think it's even worth the effort to try. The sum of all the variables that have to be "converted" to a constant in order to make a model viable would simply take the model over the acceptable limits of error and won't deliver accurate data.
What I would see possible is obtaining a relation between the benefits of mastery rating and those of crit and haste rating, based on the target's given hp%. The resulting graph should give mastery a large margin when healing a target at 1hp ( starting up from decimate effect ) and no benefits for healing someone at 90%+ hp. The relation between mastery and crit/haste should be interpreted by the amount of predicted damage in a raid and adequate reforging could be done depending on each fight's characteristics in order to maximize healing. Even if we know what to expect from a boss encounter, there are too many variables in the game that limit the precision of the guess we make when deciding to go the mastery way or the crit/haste way for a given fight.
I would like to make an additional comment, slightly off-topic, but an argument in favor of Mastery rating as the main stat for restoration shamans. Here goes:
If we are to analyze the bonus of mastery for the other 4 healer classes I think that the conclusion is clear : shamans "almost" win at overall utility of the mastery bonus and are clear winners when it comes to landing that huge GHW on a 10k hp tank.
Druid - Symbiosis is only better than Deep Healing if the target is above 50% hp, but when the target's are above 50% it's not critical to heal them and cheap, mana efficient heals can be used, thus crit and haste might be more helpful.
Discipline Priest - Shield Discipline benefits just a part of the spell arsenal, but the mastery bonus does not end up in overhealing and this is why the Discipline Priests are probably the winners of the "my mastery bonus is better" contest.
Holy Priest - Echo of Light heals for 10% of the direct heal over 6seconds - it's the same as the druid bonus, but slightly worse, since the target will probably get to 100% and the bonus healing is just wasted. In relation to a shaman this bonus is only better if the target is above 50% hp, a situation that makes the priests HoT more susceptible to overhealing.
Holy Paladin - Illuminate Healing - the bonus was probably put in place as a shield in order to limit the obscene amounts of overhealing the paladins did in WoTLK. This bonus will probably not save the tank if it's a close call, but the shield will prove very useful for normal situations where the tank is taking steady damage. The effective damage absorbed is similar to the bonus healing a shaman would get if the target is at around 60% hp.
Considering that all healers have a heavy spell - that costs about 30% base mana and has a base healing of around 7500-8000 I could conclude that in a progression raid, when raids are not on "farm status", the situations when the healers have to bring a tank or another raid member up from near death will be countless and the Mastery Bonus of the shamans will shine far more than that of the other classes ( that's while considering all healers have similar gear + skill, and that's the case in progression oriented guilds)