Agree with you on Steve Allen. I remember especially his show (syndicated by Westinghouse?) in the late '60s. Very witty. Letterman is funny in his own right, but he's basically doing the Steve Allen show (and has properly acknowledged Allen as the originator of that style).
That's strange. Letterman isn't the least bit funny to me.
As for Steve Allen, I understand that somebody in the warehouse ignorantly destroyed most of the archived film from The Tonight Show. All that is lost forever. Shame.