You need a good ground for several reasons but the short answer is that an end fed antenna is inherently unbalanced. This is because unlike a dipole, the "system" is asymetrical. In a truly balanced system, there would be negligable RF ground current flowing. Do not forget that in an end fed system, the feedline will radiate RF energy. You use a tuner to make the end of the feedline "look" like a proper load to the transmitter, this does nothing for the SWR on the feedline.
I am assuming that you would be feeding it with open wire line to minimize losses so coiling the feed line is probably not a good thing. If however, you are using a coax feedline, a choke will keep the coax from radiating but not help the efficiency at all. A proper RF ground will definately improve the efficiency of an end fed system.
HTH