Hmm...
Well, I've got a few ideas that I came up with--see how you like 'em...:D
1) Damn, them Martians sure are manoeuvrable!
The Martians get Gyroscopic Stabiliser on all vessels without any SPACE cost, but do have to increase their DV.
2) How the hell did they hit us from that far away?
Martians can get specialist versions of the Keel Bombard. Two versions I've thought off are the Heat Keel Bombard and the Smoke Keel Bombard...:D
3) We're behind them--no, wait a minute, in front of them...
Martians have all-round Primaries--so each arc allows all primary weapons to fire in that arc.
4) Even their small craft shoot further than us!
Martian FACs are allowed to use a heat ray-type light gun.
I've got costing ideas already, but Im not sharing them with you--yet Also, if you like these ideas, Im thinking of having EITHER the gyro option OR the all-round primaries--saves them from being too uber-nasty