I like the idea. I didn't look through everything but I did look through the lower level powers. Here is some feedback:
Create some new keywords to make your text a bit cleaner.
1. DA: Dragonbreath Attack (instead of str+2 or dex+2 or con+2, increase to +4/+6 etc wording)
2. [d]: Dragonbreath damage die
3. [N]: Natural weapon damage die
4. Dragonbreath Type: instead of acid, cold, fire, etc.
Snarling Bite: Way too powerful as an at-will power. Add Twin Strike or Dual Strike into the mix, and you could be attacking 4 times a round. Here is a different idea:
Snarling Bite Dragonborn Attack 1
At-will Melee 1
Standard Action
Target(s): 1 creature.
Attack: DA vs. Reflex
Hit: 1[N]. Your next DA attack against the target before the end of your next turn deals an additional [d] damage if it hits.
Draconic Rage: Seems a bit weak for a daily. I'd be tempted to make it a close burst 2, and change damage to [d]+Constitution.
Dragon Spit: To give you an example of how much simpler this power could look:
Dragonspit Dragonborn Attack 1
You spit of glob of energy at a distant opponent.
Encounter ● Dragonbreath Type
Minor Action Ranged 5
Target(s): One creature
Attack: DA vs. Reflex
Hit: 1[d] + Constitution modifier damage.
On a related note, you could make an addendum to this power and similar ranged powers that says if you have Hurl Breath feat, increase range by 5 squares.
Elemental Hide: Seems a little too powerful as an encounter power with a sustain. I'd either get rid of the sustain, or make it a daily power.
That's about all I have time for at the moment, maybe I'll take a look at the rest later. Hope this was helpful.
Edit: Grrr, I don't know why it keeps converting ["D"] to [d].