I think it is important to add in new blood. But the disadvantage to adding in new blood all the time is you can be breeding in a new problem like white tipped wings. Line breeding is the best way but there is a point before it becomes Inbreeding. Inbreeding can lead to a lot of health problems with the birds as well hatch rate problems. So it is best to make sure you know which bird came from which parent. I hope this helps. 
