I've been playing quite a bit of Alpha Strike lately, and I think that the game really needs one more "hard counter" to high movement modifiers. The AC precision ammo is fine, but one other option would really make things click for me. As it stands, I feel that arty is my best option for dealing with high Mov. and that just doesn't strike me as a balanced way to deal with the issue... at the end of the day, arty its more of a "soft counter" anyway. Simple is always better in these cases, so a mechanic that would allow you to deal less damage, (like with an AC or LRM special), but negate movement modifiers, would be an excellent tradeoff. That way, it wouldn't necessarily be desirable in every situation...and you wont be doing enough damage to "one shot" every light that crosses your path. We could have the AC precision for a universal -2 modifier, and something else (pulse laser?) for a variable boost based on Mov. values alone.
Also, I think that infantry needs a bit more nuance. I'm all for suggestions that involve having them interact with terrain and objectives in interesting and deeply tactical ways.