OK first let my say i did not play enough for a final conclusion, it may look diffrent in a week from now, but my first impression is... long story short:
Ground + Elite =15 seconds whole NPC squad -> Dead. :eek:
Ground + Advanced -> could be a tiny bit harder but it is good as it is (very annoying that they go for my turrets&generators now, i realy have to watch out for them and replace them at least once per mob! -> GOOD!)

Space + Elite = FUN long Epic Battles! YEAH!

Space + Advanced = ....mmmmh it is better then playing on default but it is not realy that much more difficult, it is not "Brain AFK" anymore but i still can manage it all pretty easy -> no chance to see the Death Penalty -> still to boring

So either i get slaughtered on Ground OR i have a boring time in Space.
Solution -> give me seperate Difficulty Sliders for Ground and Space... pretty please?
Comments
just wanted to throw the idea out there.
In theory, I would love fine-tuning everything.
In practice, it would confuse players and divide them up (currently, you can't mix difficulty settings when grouped - it's all one thing, as enemy AI is affected on harder difficulties; not to mention loot squabbles).
No worries, man. I'd like it but I don't see it happening unless you can come up with a way to overcome those hurdles.
I don't think the idea is bad to have a separate slider for ground. but like others said too whatever they do one thing is for sure. the ground combat the way it is on advance or elite is too much.