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I'd add a black lotus or 2 to help get out the dragons earlier.  Also, isn't drake umbra a bit redundant on flying dragons?

Hm...okay, first thing I have to ask is how much removal is played in your local area?  Because if it's more than 'next to none' I'm going to have to say to replace the Dragonspeaker Shaman s as they have GINORMOUS bullseyes on them.  As for what to replace them with, may I introduce you to worn powerstone .  Similar function.  Same cost. No color restrictions.  Most importantly:  MUCH harder to remove.

You're going to want more control for your deck since you're only running 12 creatures.
Oh and bump your land count to 24.  Trust me, you'll want it.

Assault strobe is decent, but unnecessary.  You are running dragons with crucibles.  They can go.
Sword of Vengeance can be dropped to a 2-of.  The only reason to keep any of them at all is for the trample they provide.
Drake Umbra is too expensive for what you want.  The buff is nice, but you are already running dragons with crucibles, they're big enough.  The flying is redundant.  If you really truly want totem armor then use either crab umbra or eel umbra .  Crab is cheaper and allows you to untap a dragon to block.  Eel can be a surprise to make them waste a removal spell.  Honestly though I'm tempted to trade them for lightning greaves .  Your call.

I honestly don't see what Mirror Sheen does for you.  Yes it's a deterrant, but that only works if you leave mana up for it and it only works on spells that target you  (not your creatures).  I think you will find that often times it sits there and does nothing since you don't have any spells of your own to take advantage of it with.

Mana Leak and Crucible can stay.

This leave 6 slots.  You really really want control here to keep you alive until you land your dragons.
If you have any I would suggest Bonfire of the Damned .  If you don't have them, don't bother, They're $30+ a piece right now.  You can run Devastation Tide or some other cheaper sweeper instead.

Your last 2-3 spells can be swerve .  It often 2-for-1's the opponent.

Oh yes and your last four lands could do to be duals.  Something like: Steam Vents or Izzet Boilerworks .

With only 12 creatures in the deck Moonveil Dragon may as well be the lower color weight shivan dragon or his better new counterpart flameblast dragon .  You simply aren't going to find yourself in the position too often of having multiple dragons on the board.

Also, there's a new dragon in M13 that may interest you:
New Dragon Show