You should try sparring with some wooden knives, or padded clubs, and see what turns up for you. It changed my whole practice, for the better!
Indeed, I intend to get some foam knives.
It would be fun and safe! I remember doing this in one of the Yoshinkan dojos I trained at and it really made you respect knives.
No matter how good my techniques against tanto-dori is, I'm not going to risk it and people should not build a false sense of security from practicing weapon taking techniques. RUN RUN RUN being the most important thing.
That being said, I was once had a robber point a knife towards my chest and I had did some sort of koto gaeshi on him before I could quite think and ended up in some sort of yonkyo lock where he was screaming and I was screaming like a little girl as I realized I didn't know what to do after I locked him. I went fully with the yonkyo, probably dislocated something as I heard something pop and a huge scream from the robber. And then kicked him in the ribs a few times before running back home like a girl. Lol hey not beautiful but it works :P
Though of course in general, if the knife guy knows what he's doing, he's in most cases going to slice u