However when something is important we usually want it the best, we don't want 100 different ways of manufacturing nails just that every factory can play special snowflake, we want one most efficient way and every factory adopting it.

Assuming we know in advance what that is, and that it won't change as circumstances change. The point of individuality is that in general the only way to find out the efficiency of a method is by trying it. Hence if a factory owner has a new crazy idea for how to manufacture nails, let him try it (without having to convince a panel in "nail manufacturing experts" first).

"Special snowflakeness" is want happens when "individuality" becomes a lost purpose. The "individuality only in irrelevant things" that you are arguing for is what happens when it becomes a really lost purpose.