My best example right now of a dirted tank is my 220g dirted that is about 2 years old now. You can view pic's via the link below in my signature.
I have run both dirted and non dirted for years and found both methods to be successful. But in dirted tanks I have always had monstrous growth (30" tall amazon swords and crypts that grew over 15" tall and equally wide) in heavy root feeders even without using root tabs very much (I am not always the best remembering to put them in). I also have never had any crypt melt in my dirted tanks. Plus the added advantage is as the organics break down in the water it helps soften the water which for the fish I keep is great. So do you need to dirt in order to have a successful tank, no. But is it worth it, to me, absolutely.