My sump is 2' deep and has never had any water in it since I bought the
house 13 years ago. When I bought the house I found the sump pump was
improperly installed and didn't work, so it hadn't been needed in the
previous 13 years either.

I have a pretty steep slope away from my walkout basement; there doesn't
seem any reason water would want to get into my basement rather than running
down the hill.

Is there any reason I shouldn't just put a wood disk over it and reclaim the
space? I just have this (irrational?) fear that the moment I do... I know
the amount of space doesn't seem like much, but when you figure out the
space the pipe requires to get to the storm drain, it could be a nice set of
shelves instead.