I agree. Forget the sprites- they should be 3D-ified along with everything else.
Just one thing with the map- the original 2D image is on an angle- to make it more overhead in the AOS version, you'll need to stretch the heightmap so it reaches the top border. You'll probably lose that little island at the top left, but I doubt anyone would be running around up there anyway.
EDIT: I'm no photoshop whiz, but this is what I mean:
Note that I've added a route around the north of the island for gameplay purposes. Now most of the first island is in the blue spawn zone, and there's now some land above the green spawn zone. Both sides have roughly the same amount of spawn area.