in GalCiv1, one of the best situations was when there was a big gap in the middle of the galaxy, so much sectors wide you had to work hard to make the recoveries early enough to reach over that gap early enough.
in GalCiv2, huge Galaxies are small compared to that...
Besides that, how long do you want to play on a map, say 36x36?Sounds like a full time gaming job
I like to play a game for one or two weeks, some hours a day. fulltime? yes, somehow.
in Civ3 I used the editor to mod the mapsize only.
really big maps, really long games, yes.
so what? nobody is forced to do this, anybody could play 12x12 maps if they want, even if the maximum is 48x48...
I hardly remember any game, where I don't use maximum map sizes... AOE, EmpireEarth, Settlers... whatever