[4E Ranger] Is Shield of Blades any good?

[Kiero]

We've just hit 8th level, and my character now looks thus:

Blend, Level 8
Human, Ranger
Fighting Style: Two-Blade Fighting Style
Background: Occupation - Criminal (+2 to Stealth)

FINAL ABILITY SCORES
Str 18, Con 14, Dex 16, Int 10, Wis 14, Cha 10.

STARTING ABILITY SCORES
Str 14, Con 14, Dex 14, Int 10, Wis 14, Cha 10.

AC: 22 Fort: 22 Reflex: 22 Will: 19
HP: 66 Surges: 8 Surge Value: 16

TRAINED SKILLS
Stealth +14, Nature +11, Endurance +11, Acrobatics +12, Athletics +13, Perception +13

UNTRAINED SKILLS
Arcana +4, Bluff +4, Diplomacy +4, Dungeoneering +6, Heal +6, History +4, Insight +6, Intimidate +4, Religion +4, Streetwise +4, Thievery +7

FEATS
Human: Action Surge
Level 1: Two-Weapon Fighting
Level 2: Two-Weapon Defense
Level 4: Weapon Focus (Axe)
Level 6: Alertness
Level 8: Quick Draw

POWERS
Bonus At-Will Power: Twin Strike
Ranger at-will 1: Nimble Strike
Ranger at-will 1: Hit and Run
Ranger encounter 1: Fox's Cunning
Ranger daily 1: Jaws of the Wolf
Ranger utility 2: Yield Ground
Ranger encounter 3: Cut and Run
Ranger daily 5: Frenzied Skirmish
Ranger utility 6: Weave Through the Fray
Ranger encounter 7: Sweeping Whirlwind

ITEMS
Adventurer's Kit, Backpack (empty), Arrows (30), Waterskin, Rations, Trail (10), Frost Battleaxe +2, Boots of Striding (heroic tier), Everlasting Provisions (heroic tier), Magic Battleaxe +2*, Magic Leather Armor +2*, Magic Longbow +2*, Amulet of Protection +2*

*Not actually magic items, but static bonuses attached to the character. Pretending they are magic items is the easiest way to get them into the CB.

He's the classic stalk around the fight and smash things skirmisher. I seem to do a lot of switching weapons, which is why I picked up Quick Draw. It also comes with a handy boost to Initiative, which is always useful as the fragile one.

Is it worth considering retraining Nimble Strike (which I hardly ever use) for Shield of Blades, to give me a defensive option when I need it?

Until recently it was always the case that the Ranger had only two at-wills worth having; Twin Strike and Hit and Run. I took Nimble Strike because Careful Attack is useless.

Is Shield of Blades a useful way of adding some survivability (AC of 24 is not too shabby) when I need it? Or just a dead end of not-Twin-Strike-ing? I would lose a little ranged utility since I can't shift away from melee as easily, but this is rarely an issue.