I believe elevation should grant ANY unit (besides aircraft), +10% armor (against ground attack) +15% damage (only against ground units).

Here are the reasons why:

1. Those of you that have played me knows how much I like air units. Because there is no such elevation bonus air units will reign supreme in multiple situations whereas ground units are much more situational. With the added bonus, now ground units have a reason to be placed properly.

2. Infantry defense will work properly. On a map like Into the Great Wide, the battle for the side resource buildings should require strategy rather than random luck. If an infantry unit is on a hill, it should be able to beat an infantry on the ground, albeit it'll cost a lot of health. Right now there is no such mechanic and an regular infantry vs. regular infantry is just a luck fest. This brings into the 3rd point.

3. This is a strategy game right? If a recon goes up against another recon, there should be something you can do, without using cards, to increase your chances of victory by just a SMALL margin. If both recons are next to a hill, the player that recognizes such difference is able to move the recon onto the hill, even for just an additional turn until the other player caught on, should be able to duke it out with better odds. OR the other player can recognize ground vs. hill is NOT a good idea and runs the Recon unit away. This adds so much more possibilities to engagement rather then right-click select chase strategy right now.

4. Part of this is also inspired by a game between Xlom and I today. We were on crossfire and he used airlift to lift a AA Hero and Artillery on the hills surrounding mid. For a while he was able to dominate whatever I threw at him (I won the game of course). Strategies like this, and airlift would be a LOT more useful if the elevation bonuses are implemented.

Potential Downsides:

This spells doom for air supremacy. With that said, games will last longer. You want to weight both sides.

Perhaps lower the %, and add a Vision increase.

Maybe 5% and 7.5%

As being on a Elevated 2-3 Hex should grant better vision.
and an extra +1 Vision on a 2 or 3 Hill, if there are 4's they can be +2.

Lee