I direct your attention to #3 above in my original post. With moonstone (or other stone materials), the armor will consist of large slabs of stone vice thinner (though maybe just as strong) sheets of hammered metal.

If the armor was only wearable by elves, I'd decrease the weight a tad - call it elvish craftmanship for elves. However, all the moonstone armor out there is wearable by everyone. Check out the description as well - it talks about the plates of moonstone and the fact that "Unfortunately, it is rather heavy."

Now that's not to say that the material of this armor won't be tweaked at some point in the future - maybe it'll be moonstone-studded mithril or something, so it can keep its special qualities but be a bit lighter. That'll come with the second round of tweaks. For now, if you don't like heavy armor, avoid moonstone - there are plenty of other good options out there.

Kastellyn the Devourer of Magic, Lord of Legends