I don't really see the need to sand a bokken, for a jo yes, since you need it to slide between your hands. I have Iwama style Kingfisher's hand cut, regular sanded finish grade 5 and enhanced. I actually like the dents and patina on my bokkens.
I suggest you go for the enhaced bokkens, save you the work of sanding since they're dent resistant and don't warp that easily.
If you never ever do kumi tachi where there is wood-on-skin contact, you are fine, but its just not cool to use a splintery bokken if you are going to touch someone's wrists or arms with it.