I'd go with your dad on the movement thing. I figure if I build 10 ultra fast ships, they can move from one battle to another in less time and it's easier to mass the ships together - avoid having singles and doubles picked off as they go to join a fleet. Someone with slower ships has a harder time amassing their ships - so I can pick off the singles and the doubles!
Also, if my movement is double his, I can essentially be in two places at once (well, close enough), meaning that I need one fleet of 10 ultra fast ships, and he needs two or three fleets of 8 slower but stronger ships just to engage me.
Well, that's what my aliens tend towards anyway.
Edit: Oh, and doesn't your brother find the mass to propulsion ratio a little low with solar sails? How 'bout a supply ship in each fleet (I'm big into ultra-specialized ships)
[ 11 May 2002, 18:31: Message edited by: jimbob ]