Good points; in answer to your last question:
If there is anyone who beleives that are are real benefits to training with live blades, I would be most interested in hearing them.
I'd answer with your opening point:
There is certainly an impact on the mindset when sharp blades are used.
IMO that shift in mindset is extremely valuable; a reinforcement that that weight in uke's hand represents a real threat.
Not for self-defence though; you're right there. So far; all the knife defences I've seen are one step from useless. Don't get me wrong, the techniques work, if
the attacker gives you time to prepare, and if
he uses the knife in a manner you've specifically trained against, and if
he has no knife training or practice himself, and if
you can overcome the instinctive horror a blade in the hands of an attacker gives you.
You'll note there are an awful lot of if
's in there. Let's be blunt: someone using a knife for attack isn't thinking about fighting; he's thinking about killing. He'll be coming with full-force; adrenaline pumping so hard his muscular strength and reactions will be at maximum; he's likely to feel no pain. And he's not going to be using fancy, preset techniques; he's most liable to be coming in from the blindside in a rush - you're not even going to see
the knife until it's residing in your kidney.
To be blunt; I see very little real defensive value in aikido knife-defence techniques.
But all that said; there's more to the techniques than defensive value, isn't there? They teach movement, control, discipline, among a great many other benefits.
Tanto techniques do help aikido in general; providing a separate element which nage must deal with. For this reason, a live blade can be an interesting addition for more senior members - lift a live blade against a yudansha and watch his smooth, polished technique break down in uncertainty in a real hurry.
As an aside; we've only used live blades in our dojo a couple of times - once when I used one as a demonstration of the risks of the tanto-dori techniques; and once when I gave one of our 3rd kyus an iaido sword for doing 'bokken kata 1' - he was a bit lax using bokken; waving it around for fun like the stick it is; so I gave him the sword to reinforce the fact it's a real, dangerous weapon. He sharpened up instantly - no pun intended. Hasn't waved it around like a baseball bat since.