Personally... I'd worry more about making one great LA nation with all stuff in there than about a 2nd MA nation.. if the LA nation is finished and very good and played a lot and you want to continue, maybe then see how you change things..
getting ONE nation that gets played a lot in MP etc will be hard enough

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Want a blend of
fantasy and
sci-fi? Try the total conversion
Dominions 3000 mod with a new and fully modded solar system map.
Dragons wanted? Try the
Dragons, Magic Incarnate nation.
New and different undead nation? Try
Souls of Shiar. Including new powerfull holy magic.
In for a whole new sort of game? Then try my scenario map
Gang Wars.