I think the simpsons should grow older as a new direction for the show. Yes you can argue that the show works because of it's agelessness it needs to do something new realistically, and I think that is the best way to go. Gradually let them all get older. Maggie could go through childhood, Lisa and Bart through puberty, maybe grampa could die. It was started as a pisstake of sitcoms so, it makes sense that they grow older now. It might not work, but it might just. There is potential financial harm in doing so though so it will never happen... oh well.