I created an ESTA in January 2014 and then entered the U.S. on that ESTA two times in 2014 and then in April 2015, in all cases in SFO. On my visit in May 2015 I found to my delight I could now use a fast lane for entering (i.e. the one that U.S. residents use with the automated computers etc.) due to it being a re-entry on the same ESTA. So the queue was much shorter that way. Now my ESTA is expiring so I will have to buy a new one for my trip end-of-February.
My question is then, can I now again go to the fast-entry line or is it "back to scratch" because it's a new ESTA? Will it make a difference if I buy the new one before or after the old one expires?