"The comparatively primitive Lunokhod was able to roll much faster - and so much farther - than today's Mars rovers for the simple reasons that Mars is much farther from the Sun"
Sort of - but it's not a power issue that caused this, rather the distance from Earth. Lunokhod was able to drive much further because it could be directly remote-controlled from Earth; the round-trip signal time was only a couple of seconds, which is not an inconvenience at a slow roll. Mars rovers have to be semi-autonomous, which means that even with sophisticated obstacle-avoidance software they are limited in how far they can safely drive each day,