Since I've been playing, I've tried to play the vast majority of my games on a standard size game play area, (6' x 3'), and I've found that not a single time, have we needed that much space. I'm convinced that 3x3 is perfectly sufficient for any game 400 points or less.
The reason is, you are typically going to be flying toward each other to try to shoot each other, so there isn't really much reason to have your ships 2 or 3 feet apart from one another. And there are 6 turns, so you don't even have time to fly that far to begin with. By the time you get close to each other or pass each other the game is about halfway over, or sometimes farther along than that, depending on speed. I just haven't seen any real reason to have a 6' x 3' play area at all yet. Never has it been necessary, we just find outselves all concentrated in a 2' x 2' section of teh play surface and have a TON of extra blank space.
Cue the Taylor Swift song 'Blank Space'.