I suspect that Six's glowing spine had more to do with the writer's trying to create some kind of effect just for us to emphasize the point that she was a Cylon and not a human. Or it could be as ViperAce suggests, her means of showing physical satisfaction.
As for the time (40 years) that it took the Cylons to increase their technology, consider that during the initial Cylon war, they must have already had some pretty good smarts or it wouldn't have been much of a war. So my guess is that they were already somewhat (if not quite abit) technologically advanced. And then consider that the Cylons are an AI race. All those AIs "computing" together has got to be some impressive computing power. So I wouldn't at all be surprised at what they were able to achieve technologically after 40 years. Heck, look at "us" at how fast we have advanced technology since 1963. Room sized computers to powerful computers that can fit in your pocket. Telephone switchboards to cell phones. 110 baud modems to multi-megabit cable modems. And on and on.