I've used 1/2" before. It's a little thin, but you do not have to route for trackballs and for joysticks it let's it sit a little higher in the control panel.
To make the edges a little thicker and a little stronger you can glue another strip of particle board along the edges. After the glue dries you can route a slot for the T-molding. You will need to either a 1/4" strip to make it 3/4" total or to use a 1" T-molding.
To do this you glue a strip along the exposed edge(s) where the T-molding is to be installed. Make sure the glue is full coverage, spread evenly, not too thick. Clamp or screw (not too close to the edge.) When it dries you can re-shape the board and route it. It's just like working with a 1" particle board.
I've used some 1/2" cabinet grade plywood for some other projects and I am contemplating using the same process for my next control panel. It's a lot stronger, flexible, and stable. Also stains well... A little curious how it will route for T-molding slot after the edges are doubled up though. My local Lowes just started selling it. The sell it in full or partial sheets for a decent price. Much better price ($30 for 4x8 sheet) than the Oak and Birch plywook commonly used.