Based on the leaderboards, here are some sales figures.
Sam and Max Save the World: 14,609 copies
Wallace and Gromit Fright of the Bumblebees: 18,118 copies
Secret of Monkey Island Special Edition: 51,813 copies
So as you can see, so far Monkey Island Special Edition has sold more copies than both of those combined.
Though I'm sure all 3 have seen substantially higher sales on PC.