hi, a good one last u a long time and u dont have to worry about limitations as compared to user some lower end models. u nv know u might need those extra features one day also. 580ex II is a good flash to invest i guess haa. or u can consider a third party nissin 866 which is very popular also.
one shot invest in a good one and u wont have to worry so much, reason being, the value of ur flash depreciate the moment u buy and use... u cant really sell for a good price i guess especially after the warrenty period. a good flash last u a long way hehe. more expensive to sell and upgrade.