For what it's worth, here is my view on this subject...

I guess everyone has their own take on this as a result of individual experiences. I have had a wing failure - most likely due to my lack of flying skills at the time, however; ever since then, I not only glass the center section (on most but not all planes), I also replace the ply joiner with a solid piece of maple. It probably also depends on the plane and type of flying you are going to do. High wing loading and/or extreme types of flying should make you want to glass the center section. If you are not going to "wring it out" or if you are just into lazy scale flying then you may not want to go through the trouble.

Steve