Bending metal "work hardens" it and leaves it more brittle. The severity and frequency of the bending contributes to work hardening.
I don't know what the original valve was heat tempered, or to what spec. But, if it was re-tempered to original specs after straightening, it should work as new. If it was simply bent back from tiny movement, it may still be within hardness tolerance.
Of course, if it has become more brittle, it has more of a tendency to snap, particularly if the race springs are used.
Hard to asses your actual risk level without some test data. What bent it in the first place? ...and how much?
I seems you are looking for a black and white answer without providing the data to make such an assessment. I can tell you from experience that a snapped off valve head can ruin a great deal of the motor. (different engine and valve type, but the results are similar)
The picture below shows parts from my Lycoming engine. I show it as a means to illustrate what happens when a valve head breaks off. I'm not saying yours will. And the Lycoming parts are certainly different from Honda.
Anyway, my mechanic told me I was lucky. If the broken portion hadn't found the exhaust port, it would have eventually beaten a hole in the piston crown and contaminated/damaged the lower end and oil supply, too. As it was, a new piston, ring, valve job, and some re-contouring of the cylinder head combustion chamber, got the engine working again. That's quite a bit cheaper than a whole new engine.
I did get the brown stains off my seat, btw.
jk
Cheers,
