Is the upgrade worth? MK4 to 4S to core plus

Hey,

I got two Prusa MK4, both run good both without any multi material.

We print a lot Multi Color (mostly 2 Color but it’s need to change) and the MK4 can just print single colour.

Is the upgrade worth one printer converting to a core plus with idex? Or just the core plus?
Or should I just get the upgrade to 4S? To improve cooling and high flow ?