Head On 2 would be great as far as the overlay goes (but vertical).
Reactor would be great, too (I've been told someone was working on a version of this with Spike as the player but enough with including Spike for everything already).
Quantum would be perfect for the analog joystick.
And not a game but I wish someone would brainstorm a trackball for the Vectrex. There must be a way to use the inputs for the joystick for that, still leaving the controller with 4 buttons. Quantum, Missile Command, Centipede, Atari Football, other games demand it!