I dunno why, but I have a strong feeling about the sniper class and dexterity when it comes to game mechanics. I always felt that operating heavy machinery is what a sniper does, and dexterity is a good thing to have for that
But this is just speculations on my part, and your idea of adding Stamina to the sniper makes much sense. I think that to fill that need I'll give all the classes an additional skill. Here's what I'm thinking:
Trooper [Class Skills: Strength, Dexterity, Reaction, Shooting, Gunfighting] + HeavyWeapon
Sniper [Class Skills: Eyesight, Agility, Dexterity, Sniping, Camouflage] + Stamina
Skirmisher [Class Skills: Reaction, Stamina, Strength, Shooting, Gunfighting] + Throwing
Sapper [Class Skills: Dexterity, Reaction, Intelligence, Sapper, HeavyWeapon] + Eyesight
Scout [Class Skills: Eyesight, Hearing, Agility, Camouflage, Stealth] + HandToHand
Medic [Class Skills: Health, Energy, Stamina, Intelligence, Medic] + Shooting
Why give the medic shooting as a class skill? Well, this class has only 1 Skill and 4 Parameter, if I added another Parameter it would mean that if this class is chosen, 3 skill points would have to be spent on the medic skill. This way it makes it more balanced and the reason for choosing this class isn't only the Intelligence Parameter this class has.