Ever swim into a wreck, turn around, and find the way back out silted out?
Ever get hung up in a monofilament fishnet?
Ever drop something like a steel double-ended drawbolt clip into the silt?
Part of the answer involves "how bad your eyes are".
Another part of the answer involves what you consider the probability to be of getting into a situation where excellent vision might be necessary to extricate yourself from the predicament.
Still another part involves possibily dropping some small expensive item that you need, and not being able to see it against the blur of the items on the bottom.
Then there is the possibility that your buddy might get into some trouble, but you may not be able to see well enough to (pick one - untangle him/her, find him/her, see the way out for both of you, etc.)
So, it depends. How bad are your eyes? What sort of diving do you do?
If you can't see well enough underwater to get yourself out of a situation you can reasonably foresee yourself getting into, perhaps perscription lenses may be a good idea.....
<FWIW, I got a Seavision mask with prescription lenses when I determined that I couldn't see well enough to discern the line from my reel against the bottom of the wreck in silty water without corrective lenses... No regrets.>