Unless there is some strong political reason to do so, like Earth keeping the
Martian colonies in line to show who is still boss of the Solar System (for the
moment), or on the other end a gesture of interplanetary goodwill on the part
of the Martians, shipping a rover back to Earth just for the sake of having a
piece of history would be most expensive, even in those times I bet.

As for preserving the rovers and all other historical craft on Mars, I would
spray some kind of clear plastic on the rovers and the immediate zone
where they finally stopped, plus perhaps certain areas they explored of
signifigance. I can see the paths they took being "roped off" by the
Martian Park Service for tourists to follow and study. Of course the
tracks may have to be recreated in certain places thanks to the Martian
winds, dust storms, dust devils, and the odd hooligan.

As for terraforming and even Dyson Shelling, then I guess somebody better
get the ancient machines off world.

Put them in the floating museum that travels the Solar System bringing
history and knowledge to all the inhabitants of the worlds.