I have the entire front end off of my 2004 MCS with 155K so as to replace the crank position sensor, the a/c compressor, the radiator, and in general to do what needs to be done at this mileage. Should I replace the 'green gasket' between the air intake tube and the supercharger outlet? It is original.

 

Some might just because...
But if it is not leaking and you don't touch the SC...I would expect you to be fine.
Never changed one...but it's rare to hear one fail unless it was a botched install....they can be tricky to get right....

 

We replace them every now and again if the SC is off, or we have the intake tract apart for other service. They start to fit less taught over time and instead of being a jamb seal they become more of a slip fit, for the money I'd replace it if it was apart.

Fit it on the supercharger inlet, then the intake duct on, and the rest of the intake tract.