Welcome, kallyn.

About Lureen's hair: I think Anne Hathaway said something about it in an interview... something about how, as time goes by, Jack turns to the liquor bottle and Lureen turns to the peroxide bottle.

But, yeah, I agree that it's a sign that the marriage is becoming more and more fake, or that Lureen is trying to find some way to become more attractive because she knows she doesn't have Jack's attention.
About the headlight: whoa! I've never heard anyone discuss that detail before, I don't think. As for reasons... hmmm. Well, partly it shows that Ennis isn't doing very well financially. And, hmmm, broken lights or electrical things. Maybe the spark isn't quite there when Ennis isn't around Jack? (Somebody else will do a better job interpreting that one, I'm sure.

) (Heh... I just read uhketchup's response, but I'll go out on a limb and make pretentious, tenuous points.

Hopefully somebody will tell me if they don't make any sense.)
And the dialogue in the 2nd tent scene is one of the Great Mysteries of the Brokeback Mountain Cult, I think. That, and how exactly Jack died. And whether Jack really quit Ennis. And...