(1) If this sort of rate offers a safety problem in terms of effects upon a human observing them, and
Doubt it, what frequency did the CAA use to try and trigger strange waves on the EEG for class 1 issuance? Probably less than 20Hz but greater than what you are proposing.
(2) If this sort of rate significantly degrades the chances of it being spotted by another aircraft.
Doubt it, I think it's the duration of the flash itself (short) that causes the attention to be caught. From distant memories of chopping up brains we use some primitive pathway in the brain, ISTR that people who are totally blind from destruction of their visual cortex in the back of their brain can "see" short flashes (google "superior colliculus" I think).