Re: Bokken - from the spine or not?
I'm not really sure how to judge answers to a question like this - largely because we are talking about aiki-ken.
The aiki-ken (yoshinkan and seidokan) that I have done enough to comment on isn't intended to prevent you from being "open" in a swordfight (or, in fact, relevant to a swordfight at all). We don't decide if aikiken is "real" or "correct" on those terms, but (I imagine) on whether it aptly teaches aiki principles or tests a student's understanding of same. From what I've seen, different teachers view buki as useful for some different - and nonoverlapping - things, so one would have to consult (imagine!) with your instructor.
Koryu weapon arts obviously have a different test (persistent historical use in battlefield engagements or duels). Two koryu weapons arts (at least) have sword strikes that initiate from well below 45 degree angles, so I'm not much swayed by contemporary arguments that such attacks aren't well thought out.