Yes, use the sagulator to check this out. It can tell you if 1" ply
deflects more or less than various solid materials.

Other ideas.

1. You could use a stronger attachment at the ends. Have you ever seen
the old cabinet technique where you have a notched piece of molding at
the front and backs of the sides (kind of looks like dentil) and you
have a loose piece of wood say 3/4x3/4x12 that spans across a selected
set of notches and the shelf sits on that? Of course this assumes you
have a face frame to hide the ends of the shelves.

2. You can add a beam under the shelf. Say a 1" wide piece of 4/4 hard
maple turned on edge half way back. Pretty un-noticable but adds a huge
amount of strength.

3. If you use solid material you can go thicker but make it "look"
thinner by using an edge treatment. I like to use a panel raising bit
(without a back cutter) or a table edge bit (like a thumbnail). If I
use the pane bit I then round over the underside front edge too.