Symetrical Levels

I actually really like the normal vs. overgrown with plants idea and that's what i would do

If you wish to see a great example of symmetrical maps that are 'different', check out Matt "Hellface" Armstrong's Darkness series for TFC. Each base has a different feel. Considering the map is like.. 5-6 years old and on a crappy engine, he did a great job with it. I've rarely seen the same thing done since. The only downside is that due to the vast differences in texturing and the slight differences in architecture, one team does gain an advantage.