Well, this is still a departure from what budo is (yes, what it's for and what's "worthwhile" about it are not the same as what it is), but...why aren't they separable from the question of why we practice? Seems to me y'all are trying to come up with unified definitions, and maybe you can, of what budo is/is for/has that's "worthwhile". But there will never be a unified answer to why we practice.
If coming to "truly understand" budo revolves around comprehending budo's purpose and perceiving what parts of budo are worthwhile or important (as Peter suggests), then it's impossible to "truly understand" budo, because it's impossible to categorically determine what budo is for and what is important about budo. We decide those things for ourselves on an individual basis; that's where the question of why we train comes in.