Yes, sorry if I wasn't clear enough. I play DL's only, so changes made in DA/TA I wouldn't know about.
To get a little further into the DL system: the Doom Ray (highest level beam weapon) has an atk value of 22, costs 150, and requires space of 10 +4%. The best shield defense, Ultimate Invulnerability, has a defense value of 9, costs 140 and requires space of 3 +3%. So you need three UI's to counter the Doom Ray. The space required is about the same for both systems, but the UI defense in total will cost nearly three times that of the DR.
The story is about the same for Mass Drivers and Missiles. It will cost 2 1/2 times more to counter the Blackhole Eruptor missile, and close to three times as much to counter the Black Hole Generator mass driver.
The time factor required to build a more expensive starship led me to just dispense with defense altogether, at that point, go all attack, and attempt to outproduce my adversary. If I can produce three mediums or four smalls while my opponent is building one BB/Dreadnought or two mediums, I will win.
@ jakecaptiva
I get rather bored with endgame play, but for a different reason. Usually, when you get to the last three of four civs, a big "Mexican Standoff" results. Everyone is allied to everyone else, and noone wants to make the first move and have to fight all the others at once. If I make the first move even though one of those civs was my ally from way back in mid-game, they will fight for the other side. It then just becomes a huge attrition slugfest. Every DL game I've played ends up this way, so I just start another game.