Okay so this idea will not work for every gunslinger, however I think it will work for the musket using gunslinger at least:
When I was thinking that there was a chance I would make it to round two of superstar I was working on a ranger archetype called the marksman. I think the primary ability I was going for on them could work for here.
Aim: As a full round action the gunslinger may make a single attack. If this attack hits it deals x2 damage. At level 7 the gunslinger the damage is instead increased to x3 damage, and at level 14 the damage increases again to x4.
Basically the gunslinger would get a ranged version of charging with a lance. he takes careful aim and shoots only once but gets an increasing amount of damage to make up for the lack of iterative attacks.
Yeah, I posted a similar thread. I was trying to work out a way for the gunslinger to use vital strike to put out decent damage with a single shot per round and still be able to move.
Your idea works better for a sniper, my was more oriented toward a pistol and sword swashbuckler type.
Either way, I think the way to go is.
1. Have the gunslinger do 1 shot per round that does competative damage.
2. Remove the touch attack. If you only have 1 shot a round, it is going to hit 80-90% of the time. Making it a touch attack has too many weird side effects.
Anyone? Buller?