With the diapers you have now, do you think they are less soft than they were when you first washed them? If that is the case, you might have build up in them. Stiffness can happen from build up over time and would need to be stripped. It also happens when you line dry.
But if you want a reason to get something new...go for it. I agree with pp. Getting fitteds might be the way to go. There are some really nice ones on HC. BG also has bamboo ones that are fairly nice.