Help tweaking this Relentless Assault Dragon Deck

First, what help are you looking for in specific? Is the deck not running fast enough, are you looking for more focus, or something else? I've compiled a list of things I'd personally alter below, but it may or may not be the kind of change you're looking for.

Second, casual dragon decks are an asston of fun to play. I played with a rather crude version about 7 years ago, but it was still one of the most enjoyable casual decks I've ever used. I love Kilnmouth, and most of my games ended up being won using him because he can hit the player directly.

The dragonspeakers are going to be a source of extreme aggression from the opposing team; be prepared for them to be burned as fast as you can place them down. You may want to consider replacing them with Urza's Incubator (or at least keeping them on sideline). Same cost as dragonspeakers, but will force people to sideline spells to destroy artifacts if they care that much. You could also run both (4 Urzas, 2 Dragonspeakers), and then you have a 1/10 chance of drawing a spell reduction each draw. If you elect to draw, by turn 3, you'll have drawn ten cards and will more than likely be playing dragons for an extremely reduced cost.

A couple of dragons I like:
Archwing Dragon - returns to hand and cheap; couples really well with Kilnmouth. Will also play extremely well with Scourge of Valkas since it will keep coming into play. Speaking of Scourge, I would recommend playing two of him as opposed to one. He deals directly to the player, which I have always found to be crucial for fast game-wins even in a pickle.
Knollspine Dragon - given you're going the multiple combat/main phase root, when this guy enters the battlefield you can drawn and play a lot of cards (such as lands) and just keep cycling through. In addition, by the time he's out on the field, you'll have been/will be playing a lot of spells during your turns, which means you will probably have no hand more than you'll have any valuable cards in your hand.

Spells:
I'd pull out the Seize the Days. They only untap one creature, but they still cost four mana. You already have relentless assault and aggravated assault and a dragon to allow you to take multiple combat phases. Even without it, by turn four, you should have statistically drawn some method of having a second combat, and they'll allow you to untap all of your creatures as opposed to just one. This frees up two cards slots for things like Urza's Incubator.

I'm curious as to if the Crucible of Fire will work well or not. I feel reluctant to pull it because it's a massive beef, but it seems like its almost unneeded with how big dragons are on their own. One to test, for sure.

Also curious on Sarkhan. He feels like another needless beef; I'm sure he'll work fine, but will he be a gamechanger? Dragons are already huge, so the it feels a little redundant to make them bigger. Again, something I would pull for either a spell reduction, a dragon, or cards that would get me more lands.

The Xenagos could be excellent because of the high mana costs and of course his -6 power which can flood the field with dragons. My biggest concern with him is that he may not be very useful early in the game, since dragon decks are notoriously slow to get creatures on the field, and early game is exactly when you'd want him to be useful. This is one I'd want to try out via proxy to see just how effective he was before officially adding.

Looks like you have a great start here, you just need to balance some card-purpose to draw-statistics. Would love to hear how the deck does when you get around to playing a match.