The only thing Nintendo needs to do is get the games out in a reasonable time. If they start to do that, then they\'ll be fine. The GBA makes enough money to keep Nintendo alive through-out some of the worst times. Not to mention, once Pokemon, Mario and Zelda come out, the GC sales will rise a lot.
Nintendo is smart for not going all out and targeting the mature audience. Sony and MS are fighting for that right now, if Nintendo entered that "market" it would be a no-win situation and they would risk losing more money. However, if they just release one or two mature titles here and there (Eternal Darkness,etc) and then let third party developers such as Capcom put some mature titles out, they will be okay. It isn\'t as if anyone else is targeting the younger audience, so this is just gurantee\'d sales for Nintendo once they start pumping the titles out (which, as I mentioned is their only massive fault and the reason for slow GC sales).