Having the DS as powerful as the N64 is both good news and bad news. The good news is obvious, it's powerful. Even though they say it's not in direct competiton with the PSP or whatever, I'm sure many people will compare between the two, (at least until alot of information is revealed. If you have just the system specifications of both pieces of hardware, there will be much comparing) and having something powerful is alwasy a plus, unless it sacrifices something like battery consumption.
The bad news is more personal. If the DS is like the N64 I will feel like it IS the GBA successor and I am not ready for that. But my fears are most likely groundless. If it IS as powerful as the N64, I doubt it wil be in the same way. What I mean is, I don't think it will be something that developers can port over N64 games to. That's why it isn't a direct competitor, but a "third pillar" as they call it. The DS wil lbe somehting completely unique that will serve a purpose that none of us have already guessed.
Or not. Dunno.