I would share your same sentiment regarding injector renewal,with some at £3-400 per injector it is quite worrying what the cost would be. Did the person who advised this have a good reason why he/she recommended they be changed. The injectors I have come across involved bad starting/misfires etc and before renewing yours I would be making sure other items were checked first.You don`t say if you have had the motor plugged into a code reader but would be checking all your intake system is ok with filters,egr valves,hoses,turbos checked.Trying to diagnose problems on modern veh`s can be a nightmare and can run into big money if you guess one item after another and get nowhere fast but would ask around and try googling etc before jumping in renewing all and sundry. Good luck.
cdc, February 2015