You more or less have a point, however in several scenes in Galactica, Six's spine lit up. There's also the extreme strength and agility that a humanoid woman of that build simply could NOT accomplish without robotic enhancement, such as a titanium bone structure and microscopic cell reinforcement in musculature, etc. Therefore, humanoid Cylons are not, in fact, entirely human. Zoey's form was as you said, something like a prequel of things to come.
I do apologize if anything I've said makes very little sense. It's late, and I have not had much coffee tonight. Actually... none at all... *twitch* 
Humans are capable, you and I, of super strength. We've all heard of the mothers who will lift a crashed car off their children.
It's been scientifically proven, our muscles are capable of far greater strengths than our brains normally coax them to. This is true for everyone, probably even those World's Strongest Man competitors who pul Diesel locomotives unaided. Our nervous system evolved dampeners to stop us from injuring ourselves by over taxing our muscles. We could probably tear a muscle from the surrounding tissue at will if we hadn't got these nerve impulse dampeners.
I can't remember the specifics of the experiment, but it involved Chimps, because the dampeners aren't as advanced in them. Apparently a side effect of the dampeners was fine motor control, such as that I'm using to type this.
Anyway, supposedly, super-duper-extreme-mega emotional trauma, such as a mother seeing their child get crushed, or a child seeing their parent drowning, can override the dampening for a short time, giving them super strength, and probable injuries.
Perhaps the Cylon Synthetic Cells were made of slightly stronger stuff, with less dampening of strength. And, to be fair, Galactica was fairly inconsistent with the whole Cylon Super Strength thing. Perhaps they weren't always able to do it. As for the glowing spine... nanites in the spinal cord? Artistic license? Later in the series, the glowing spine motif disappeared, it was only really seen in season 1.