I've gone with gravitational turrets instead. Note I'm playing on Diff 10, there's simply too many units in a wave to make tractors effective.
The first wave that hit me at the 15-20 minute mark had about 200-300 units (can't remember exactly), the 2000 unit wave about to hit me is a little smaller then average for this point in the game. One of the ships unlocked the AI has unlocked is Laser Gatlings which is a high cap unit. I got hit by one of those earlier, the total wave size was 5500 ships.
In theory I could build enough tractors to grab that many ships, but I can't afford the energy, not at 500 to 1000 energy per turret, times the hundreds of turrets I would need. The rebuild costs would be prohibitive also. With that many ships in the wave, I'm looking at losing dozens of tractor turrets every time a wave spawns in.
It's actually one of the neat things about this game, the strategies you use change as the difficulty level changes. While the tactics I'm using in this game could be used in a game with a lower difficulty setting, they would be horribly inefficient and not the correct way to go about it at that level.
D.