I'm aware that B-17s attacked Japanese Shipping during WW2
(battle of Midway comes to mind), but that they were way too
high and didn't hit anything.

Speaking hypothetically, would it have radically improved anthing
if the B-17 attacked from a much lower altitude?

I'm thinking that the B-17 was a pretty tough plane, as proven
over bombing raids in Europe. And wonder if it could
survive the AA and CAP that the Japanese put up that so easily
downed the Vindicators? Speed and multiple engines come to
mind.

Still, would bombing accuracy have improved to a point that
hitting a Japanses CV would have been possible.

I have this (crazy?) picture of a B-17 lining up with a Japanese
carrier (lengthwise) and dropping a stick of bombs on it. Wonder
what the spread would be at different speeds and the intervals
between bombs. Thanks, to the SBDs, this was not needed, but
just curious.

Come to think of it, the Carriers would and did perform evasive
movements, so skip that requirement that the B-17 would
line up with the keel of the carriers.