The Tron idea is so obvious I’m not really sure why I haven’t already thought of that!

I’m not too sure if the Missile idea would work, but I might as well try it to see if it plays well.

My main problem at this moment in time is trying to achieve enough graphics for all the pickups.
Pacman’s pickups would be fruit, but there’s no fruit sprites.
To keep things simple, it’d be easier to have colored blocks, with letters or numbers on them, like the ones in Snake. Simplicity being the key.. but.. could you tell what all the different pickups do, just from one single color+letter combo? Only one way to find out!

Q-Bert Plus: allow dropping of 1 or 2 mines per level – if enemies or Q-Bert hits them, they die.

Missile Command Plus: be able to move your bases left and right using the control pad while defending them…maybe limit it to one or two bases?

Tron Plus: allow one shot per level to break through an existing line?

Pac-Man Plus: maybe implement the changes of Bally-Midway’s Pac-Man Plus? “The most significant changes in the gameplay is that eating a bonus “fruit” causes the ghosts to become vulnerable and invisible, doubling the score for eating them; and that eating energizers would often have unpredictable effects (such as turning only three ghosts blue or turning the maze invisible).” (Wikipedia)