For me Star Fox needs to do more than just become good again. I need a very exceptional Star Fox game to grab my attention and win me back. And that's just how things are when something loses me. When a franchise goes off the rails it loses my trust and my interest. If Nintendo announces a new Star Fox game I won't pay much attention to it. I won't assume that it's worth my effort to look into. And it's not because I'm mean or stubborn it's just how things work. I can only pay attention to so many things at once. Star Fox, like Sonic, currently equals TEH SUCK in my mind, so I don't pay much attention to it anymore. It's almost a sub-conscience thing.
So to grab me and make me pay attention so that I even know that Star Fox is good again, it has to be this big GOTY kind of game. It has to be as good as Star Fox 64. If all you hear is "it's better than Assault" or "it's pretty good except for..." it won't do it for me. Those are wishy-washy apoligetic prasies. It has to win over the skeptics, not the die-hards who will try to find enjoyment no matter what.
A minor example would be Super Mario Galaxy. Super Mario Sunshine was not the best. It was still very good and it was just one mis-step so it's not the best example. But it was enough that there was concern. But Galaxy, from just the first footage, was so HUGE that it grabbed my full attention. And, hey, the main Mario series is back in the saddle. That's what I need. I need a "holy ****, Star Fox is back" kind of game, not a "oh this new Star Fox is supposed to not suck as much."
Though I can't tell if Miyamoto is trying to put a positive spin on things or has Nintendo really not put the pieces together? It's quite damn obvious why Star Fox doesn't sell so well but does Miyamoto understand that or is it a mystery to him? I don't expect him to publicly say "our more recent games sucked and that's why they didn't sell so well" but I certainly hope that Nintendo understands that THAT is the reason.