If I were you, I'd take a tent. Its definitely worth it, especially with two people. I slept in my jeep at COfest, and I wouldn't do it again unless I had to.
First of all, I took out the rear bench and folded the back down and the front seats folded (2 door), and slept diagonally, and it was still too small. And I'm only 5'9"ish. That'd really suck with two people. I've also slept in the front seats and on the rear bench and those are even worse.
Second, your jeep will smell like butt when your done. I showered every day at COfest and had the windows open all the time except for when I was in it sleeping, and it still stunk.
And third, its a pita to have to find/make room in the thing every night... if you move it to another part in the jeep, you probably will have to move it out of the way again when you go to drive it. Or you can unload all the crap in the back when you need to, but then you have to worry about it being outside because of weather/people/animals/etc. and you may need to load stuff up again in the mornings if you need it on the trail. And you'll need to move your sleeping back or blankets or whatever out of the way when you put your trail stuff back in.
Trust me, bringing the tent is definitely worth the extra space it takes up when packed and the time spent setting it up/taking it down.
