In my experience, missiles/torpedoes are almost always worth its price. In my 100 point Alliance list I use Garven Dreis/Dutch Vander with R5-K6 combo, both with torpedoes. How it works?
Garven moves first (they share the same skill of 6), gets Focus token. Dutch follows, acquiring Target Lock, and so does Garven. Then an X-wing fires first, possibly using his focus, granting it to… Y-wing, who then proceeds with his volley (to boot, after you spend your Lock to fire torpedoes with Vander, R5-K6 can immediately get you another one you can use to re-roll… and then Garven gets another too!). Depending on who you shoot at, the result of the salvo should be either one destroyed TIE, or one close-to-be-destroyed TIE, or two scratched TIE's (if you acquired Locks on diffrent ships).
The third ship in this squadron is Luke. He usually softens one of the ships I plan to bombard with torpedoes, possibly using up enemy Focus or Evade that can thwart my plan.
Also, the Missiles upgrades works really well.
However, I must admit I consider Concussion Missiles to be superior. First of all, you get to change one of your blanks into the hit. That's huge bonus, since you should have Focus anyways, so you should not worry about any eyes rolled. An ideal salvo should get you four hits. Against both X-wing and Y-wing it means at least it shields are down. Even if you score three hits there's still chance for the failed roll on the opponent's side.
When shooting Cluster Missiles:
A) you have to be firing on closer range, and you want to spend your Focus on the attack, so without extra dice for being at Range 3 you're more exposed to enemy's retaliation or pre-emptive strike.
B) you can use your Focus for only one of the two three-diced rolls, so if you roll eyes on both, you're not able to do anything about it.
C) if you roll blank, than you can do nothing about it.
D) your opponent gets to roll twice; of course he also can use Focus on only one of his rolls. This calculates better against an Y-wing, since you roll 4 attack dice more then he rolls defence dice, but against an X-wing you get only 2 more dice, and you hit less reliably.
To sum up: using Cluster Missiles is more based on your good rolls, calculates better against an Y-wing and requires you to get closer. Concussion Missiles let you hit your enemy more reliably while staying further.
Of course you can fire from outside the enemy's ships' firing arcs, but secondary weapons are usually fired early-on for maximum damage and quick elimination. And, if you keep your Missiles/Torpedoes for mid-late game you risk being shot down without firing it.