That's difficult to say for sure, however I don't think it's worth retaking the GRE just to boost your writing score. A quantitative score of 800 is perfect, a verbal score of 710 is very good, and a writing score of 4.0 is decent (though I know disappointing). Physics departments will put more emphasis on your quantitative and subject test scores anyhow. Though of course that's not to say the verbal and writing scores are meaningless. You can see a related post I wrote about this here:
http://www.physicsgre.com/forum/viewtop ... ight=#1527
Personally, I don't think it's worth jeopardizing your math and verbal score just in hopes of improving your analytical writing. I'd seriously doubt an admissions committee, even at the top schools, would reject an applicant based solely upon their writing score (unless perhaps if it's < 3.0). So to answer your question: no, I don't think you should retake the GRE general even if you go from a 4.0 to a 5.5. As long as your subject GRE score is solid (much more important), your GPA is high, and you have some good undergraduate research, you should be a competitive applicant.
Hope this helps! ^_^
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