It is said to have a positive effect on the quality of your beer, I do not have the capability for full boils so I cannot comment on this personally. You will definitely get better hop utilization from a full volume boil. I say go ahead and do it but you would also need a wort chiller to cool the larger volume of wort effectively. Takes a long time with an ice bath for 5 gal.
"Whoever makes a poor beer shall be transferred to the dung-hill"
-Edict, City of Danzig, 11th Century