The N64 didn't fail because of its graphics, it failed because Nintendo shot the poor system in the foot from day 1 by tying it to cartridges only.
The N64's graphical prowess was probably one reason it didn't flop altogether, there were long stretches where it would get maybe 1 or 2 games a month at best for $70-$80 a pop and virtually every major release planned for the system went through delays.
The GameCube didn't fail because of its supberb graphical ability.
The GameCube failed because it looked like a Fisher Price lunchbox (especially the purple lead model) which reinforced every childish stereotype about Nintendo and their 1st party software failed to sell the console (only time ever Nintendo has failed in this regard). Super Mario Sunshine, Zelda: Wind Waker, Mario Kart: Double Dash, and DK: Jungle Beat were not the Mario 64, Zelda: OoT, Mario Kart 64, and DKC sequels people wanted. Metroid Prime was a critical triumph but not the commercial, mass-market blockbuster that GoldenEye was either.
The GameCube was also released way too late -- 18 months headstart for Sony was way too much and just barely getting to market before Microsoft who really only started working on the XBox in earnest in 2000 and had no game console experience ... wasn't good.
Bottom line: N64 would've smoked the Playstation if Nintendo had compromised and integrated CD-ROM into the N64 chasis. Would've made the system slightly more expensive to start with, but the system was sold out for the first few months anyway.
GameCube should've launched in 2000, thus burying the XBox and not letting Sony have too long of a headstart. The design should've been a bit more adult-appealling and Nintendo probably should've put their foot down with too much experimentation with classic franchises.
None of this has anything to do with the chipset.
