Here's my take on Proton Torpedo utility;
Always remember, using the Torpedo does NOT count as your action for the turn, so this lets you make use of a few scenarios to fire it off;
1)Move, Target Lock, Fire, all in one turn
2)Move, Focus, Fire (target lock acquired on a previous turn)
3)Move, Marksmanship, Fire (create potentially 2 critical hits if you get enough "focus" results on your 4 attack die)
4)Koiogran Turn, No Action (from the stress token you just got), Fire
…or basically make use of them on any turn you have a stress token, to get a decent volley of damage when you cannot focus or use another ability that requires an Action.
This can severely cripple TIE Fighters, and if used on a ship with your second-highest pilot skill, can put a hurting on a TIE Advanced that has already had its shields softened up or removed entirely by a previous attack that turn.
The Torpedos are great against Dark Curse, because the penalty that ship provides to your ability to attack it with the help of Focus tokens and rerolls is entirely bypassed by the Torpedos. I believe there is also a TIE Fighter pilot in the TIE Fighter expansion that can cancel the effects of a damage card that is dealt face up with the Pilot Resource. If someone has the card, or knows what I'm talking about, please expand upon it. Either way, that's the only TIE's hull that won't take a serious pounding from the Torpedos, and even then, it's less than half the time.
At this stage of the game, the Proton Torpedo is not a useless upgrade at all. I think the division of opinions comes from the fact that the apparently small number of ship types (2 per side) actually provides a lot of customizing options, so our individual tastes and play styles are really taking over here. Time will ultimately tell how useful the Torpedo will continue to be, with future expansion ships and pilots on the horizon, but for now, I would stand in the camp that it is certainly worth the points if applied correctly.