Here are my thoughts after playing the Demo. I just noticed this game and have never played AW. Keep in mind I have only messed around with this XBLA game for less than 30 minutes and I am sure a developer that has spend months on it will be much more informative.
I believe Power is based off the amount of damage you do (number of vehicles destroyed and HP/Unit).
Tactics is based off the damage you receive (number of Vehicles lost and damage at the end of the Mission on your remaining units).
I just played the first two missions.
1st play through ever for this game on M1: goofing around learning the units S1, P5, T3
2nd play though on M1: just trying to finish fast S5, P5, T3
3rd play though on M1: trying for Tactics S1, P5, T5
Just a note to get the Tactics 5 Star I only used the Scout for Combat and I picked up both Health packs.
Now all three Statistics read 5 Stars. It should be fairly easy to get 5 stars on all the missions with two plays.