No... I think you need to be very careful there. While the map is larger, empires are still only formed around cities, which will (almost always) be situated in a rough design about the capital. Further, with more civs in the game, the map may well fill up much faster than you'd think.
However, the overall most important overriding factor is wartime. Giving Infantry 3 movement points makes them absolutely insane - able to attack an enemy city instantly from 3 tiles away, even outside the border. The fact is, the travel time is comparitively longer on a huge map - but that's the way it's
supposed to be. If you start fiddling with the values for movement and such of various units, you're undoing all the careful testing that put those values in there in the first place!

(And then think of the cavalry and tanks... what, 6 movement points???

An unstoppable tide!)
In summary, IMHO people play huger maps
because they take longer to play. You shouldn't need to try to balance that up by making units move faster.
(The one exception to this rule that I would agree with is naval and air units - these work differently to land units, and as such their movement range
can, and probably should, be increased. But don't touch land units!)