First off the bat, Daggermaster was updated in the Class Compendium to only work on Rogue and Daggermaster powers, so it's no longer a good choice for non-rogues (or even for rogues who poach powers from other classes). If you're really committed to expanded crit range, and you can convince your DM to permit you a Melegaunt's Darkblade (it's from a Dungeon adventure, which is why it might take some convincing), that plus the Honorable Blade PP will give you 19-20 crit range plus your breath type (presumably lightning?) on everything. Also note that Thunderbolt Weapon is available in Dagger, gives you a better Daily power, and is available at 13+ instead of 15+
With that in mind, if the reason you went Dex was to pick up Daggermaster, I'd probably be a Bozak and be a Dragon Soul sorcerer instead, and get that nice +1/2/3 racial bonus to arcane attacks. You lose the +4 interrupt from Storm Sorcerer, but Sudden Scales boosts up to like +8 at your level and Adamantine Echo is a +5 bonus to AC all encounter long.
Powers-
At will- why chaos bolt? It does literally nothing for you that Acid Orb doesn't. I'd go for Burning Spray or Blazing Starfall as your second at will (the former more heavily if you go STR/Dragon Sorcerer), or if you have a DM that grants a lot of MBAs, Ensorcelled Blade.
Encounter- Explosive Pyre is a lovely power. Flame Spiral should be in here unless you're actively avoiding optimization. Spark Form is a nice multi-attack with movement baked in, Lightning Cuts is a nice minor action attack, and Thundering Gust is lousy in general but works beautifully with Flame Spiral (or potentially Explosive Pyre).
Dailies- Slaad's Gambit is great. For level 9, I'd go either Prime the Fire (almost guaranteed 2 damage instances- and if you don't get 2, even better), or Thunder Leap (don't let the movement fool you, you can target the same enemies the second go round). Or, as noted, Adamantine Echo if you switch to Dragon Sorc/STR. TBH, everything at 1 is relatively bad.
Utilities- Sudden Scales is solid, though much better on a Dragon Sorc build. Dragonflame Mantle is ok, though I find it underwhelming in actual play- do remember that it's arcane and so gets your 2+Dex bonus from your class feature (it's not an implement power, though). I like Spatial Trip there, but Dragonflame Mantle is definitely decent enough. For level 10...Sorcerous Pulse is sort of a trap. Roll twice and take the higher is ok, and it might help you sometimes if you roll some 1s, but on average it doesn't actually increase your damage that much. I prefer Maiden's Waking most of the time, though if you end up training Bluff, Stall Tactics is a lot of fun once per day.
Feats- You're level 11 now. Sub out Raging Storm for Lightning Soul. Implement Expertise and Versatile Expertise don't stack, and given that all of your attacks are Arcane, White Lotus Dueling Expertise gets you expertise bonuses and proficiency in another arcane implement type, or War Wizard's Expertise gets you a -5 to attack against your allies if you have anything unfriendly. That should free up some feat space- if you pick up an off hand implement, maybe Dual Implement Expertise, maybe Superior Will.
Items- as noted, Thunderbolt instead of Lightning. Darkleaf Armor is fine, but I prefer Shimmering.
Paragon Paths- as noted, Daggermaster doesn't work. Melegaunt + Honorable Blade will get you damage type change and 19-20 crit range. Demonskin Adept is an easy go-to. Lightning Fury is nice on a Storm Sorcerer. I occasionally go with MC Warlock (Pact Initiate) and Long Night Scion- it's mostly useless, but the F11 and AP feature together allow you to drop an additional attack on your enemy on an action point. Bard + Voice of Thunder instead is an interesting option- the E11 is poorly written and allows you to make the attack each round as long as you hit the round before.
