I'm a little mystified with the purpose of the questioning, Paul. If i understand correctly, you want to uncover the historical validity (or its practical effectiveness at its point of origin) of aikido techniques in order to help you decide if you should continue with aikido or stick to judo. It seems to me that those are separate questions: where it comes from, as opposed to why i should or should not do it. You can uncover the historical origins for the iaido kata, but it wouldn't help one decide if one should practice it or not.
In short, I feel like I shouldn't be practicing something (or perhaps more accurately, can't meaningfully practice something) unless I have some clue what I'm doing.
Imagine if judo throws were practiced as slow-motion tai chi type solo movements, and there was no concept of randori or paired practice. It might not even be clear that you were practicing throws: people might assume they were peculiar strikes. It'd be very hard to really understand judo, because you'd have no idea where the movements came from. "Is this really a good kick?" you might skeptically ask about o-soto-gari, seeing only a forward leg swing followed by a return. You might practice a forward reaping motion into a bag repeatedly, and be frustrated with why these kicking movements didn't seem to resemble anything like good kicking technique. "I guess it looks kind of like a knee strike, if I bend my leg" you think, but then you notice that from the beginning of time people have been told to practice with a straight leg, and none of the other elements of striking are taught. Needless to say, there'd almost certainly be no good judoka around.
Once you say, "These are ways for two people in jackets to throw each other", the light bulb goes on, and it becomes clear how to evaluate your technique. You stop throwing your leg forward at the bag. You no longer feel like you have a stupidly stylized kicking method; you have a perfectly functional and effective reaping method.
As has been observed repeatedly in the "aikido doesn't work oh noes" threads, nobody's ever been able to show that aikido techniques are functional in an empty-handed contest. So clearly, practicing aikido with the idea that you're learning how to throw an unarmed, keikogi-wearing person ("gi grappling") or an unarmed, lightly-clothed person ("no-gi grappling") with these techniques is as flawed as practicing osotogari against a bag thinking you're learning how to kick.
My thinking is that maybe aikido techniques are, as people have argued, an advanced grappling principles study, that gives you some new insights and some extra techniques for special situations. If it's an advanced grappling study, then you should probably understand basic grappling first.
An alternate theory is that aikido has something to do with koryu weapons methods; perhaps rather than a principles study, aikido techniques are just as "literal" as osotogari, as in, "if someone grabs your shoulder to stab you, katamochi ikkyo is a good counter; practice this by having someone grab your shoulder to stab you." If that's true, then it's possible that judo is totally irrelevant; what's really needed is some greater clarity of training methods, creating a freestyle format without excessive rules that pressure-tests aikido skills.
Does that make some sense? In short, I view the questions as interconnected because studying aikido without any idea what the function of the techniques is (throw, knife take away, knife retention, sword take away, sword retention, etc.) seems hopelessly inefficient.