Effective edge is again a different measurement than running surface. It takes into account the board's sidecut, so if for instance you have two boards with identical running surface but with different sidecut depth, the board with the deeper sidecut will have a longer effective edge.
You are going to get different answers to your question about spin resistance etc from being on a slightly longer/shorter board. My answer is that when you are talking 2-4 cm of tip/tail shaping, you will be hard pressed to feel any difference at all. Weight has a lot more to do with construction than length.
As for base materials, riders have become a lot more informed as to the relative benefits of the different base materials. Manufacturers are meeting their requests with the best base for the type of riding. Extruded bases are a great choice for hard riding and for those who in reality do little or no base tuning.