Tough question ! This is a very personal decision and vary widely from person to person. I retook my GMAT after scoring 710 in my first attempt, even though almost all ppl said not to bother with a retake. My thot process was the following:
1. 710 was the worst score I got compared to my practice scores (except KAP).From the get-go in the test, I was having a bad day, starting from a bad overcrowded test centre.
2. Realized number of mistakes I made in my first attempt.
3. I belong to hyper competitive indian pool where avg GMAT is 750 -- this may be a myth, but cudn't leave it upto just chances.
See this thread, where I talked abt what changes I made in my prep for 2nd attempt.
Good luck in whatever u decide !