There is a single "platform" prefab that I instance. Whenever the player reaches a "record" height (a multiple of 320), a random number of platforms(at least 3 or 4, I think) is generated within the 320 pixels. 320 is divided by the number of platforms to create a "spread", so that they are reachable and not haphazardly placed.
The platform is 64 pixels in width, and the screen itself is 512 pixels wide, so 512/64 = 8 possible spaces for a platform to spawn. I place platforms in multiples of 64(in a sort of "grid" if you will), and make sure that they are no more than 2 spaces apart, and not right above or directly next to the previous spawn position.
I hope that makes sense.