If you suddenly added any kind of advantage to SC as it is now, of course it would unbalance the game. That's not a good argument. There are many other factors in SC2 that are not in SC1, so placing one SC2 feature in SC1 will not be balanced.If, in regular sc, Creep suddenly provided a 30% movespeed bonus, zerg would be unkillable in a defensive situation.
Are we talking SC2 now or are we still on SC1? In SC1, Sunkens do Explosive (40dmg becomes 20 against a Marine).as Sunkens do Normal damage,
Depends how the Marines end up targetting. 6x4 = 24dmg - 4 per armor point of target, though Marine damage can also be upgraded (9x4 = 36 normal damage vs ground & air). You also mustn't forget that although both Bunker and Sunken have 300hp, when a Bunker dies you still have all Marines (and the Bunker can be repaired).as opposed to bunkers whose dps will be spread out and highly ineffective against units larger than a handful of zerglings.
Terrans can defend very well (throw in some Spider Mines for added flavor). Zerg defenses can be potent, but they are not the best. As they say, the best defense is a good offense, and that's really where the Zerg's defense in SC1 comes from. Speed-Creep further supports the fact that Zerg defense is much more unit-reliant.
You bring up a key word: counters, a way to achieve balance. Here's an idea: A way for each race to kill creep. Say, Irradiate for Terrans rapidly shrinks back creep. As they say, there's more than one way to skin a cat. + Speed creates additional gameplay opportunities. Why waste that? If it'll cause imbalance, instead of instinctively rescinding the idea, think of ways that it could actually work, what would be needed, etc.Now imagine those infested terrans moving as fast as a crackling. What is your counter against infested terrans? killing them before they get to you. What is your counter against cracklings? Killing them before they get to you.