If you're looking to make the forums more mobile-friendly then my absolute first suggestion would be to get rid of those damned thread back/forward buttons that pop up on the sides of the screen: they are very easy to hit by accident on a touchscreen, especially since they're given to popping up out of nowhere, and worse still they don't even serve a particularly helpful purpose.
As for post headers, I think the best way of minimising them would be to get rid of the totally-superfluous individual titles, or make them default to a blank field, and leave the post date etc. as they were.