So last night I had some extra ability points and decided I'd check the benefit of pumping some points into armor specialist on my tank. According to the tooltip, Armor Specialist gives a +5% armor rating bonus and reduces the movement penalty of heavy armors by 20% per point.
Results were not what I was expecting:
Level 14 (using boosted (with anvil) body armor)
1 point in Armor Specialist: 89 armor rating, 2.40 movement
Increasing Armor Specialist from 1 point to 3 points should be a total bonus of 15% armor rating and 60% movement penalty reduction.
Level 14 (using boosted (with anvil) body armor)
3 points in Armor Specialist: 102 armor rating, 2.40 movement (unchanged by extra points)
As you can see, the movement penalty wasn't reduced at all. I assume that this is due to my crafter/blacksmith boost (armor + anvil = +movement) on this particular set of armor.
Still, I wonder whether it'd make a difference if I had 3 points in armor specialist prior to boosting my armor with an anvil--would that result in a higher movement speed bonus with the boost? I'm not sure, since it seems the +movement bonus you get from crafting gives a static +movement bonus--that is, when I boosted one set of mail armor, it gave me a +.10 movement boost, then I boosted a set of full plate and it gave me a +.10 movement boost. It didn't seem to matter what the initial movement penalty of the armor was.
If the way that crafting boosts work is not based off of the initial movement penalty, and instead just gives a static +.10 or whatever bonus, then armor specialist has no effect if you boost your armor through crafting. If that's the case, you may want to save the points and just use crafting instead.