I think Metroid Prime 4 should obviously be one of the big titles Nintendo is promoting through Directs once Nintendo feels ready to reveal the title, but I think a campaign beyond online ads (TV spots, billboards, etc.) would see diminishing returns. If Nintendo spends too much on marketing that Metroid Prime 4 doesn't break even, that would be bad news for the franchise. All it takes is for one glorious flop to put a franchise on ice. Just ask EA and its graveyard of IPs like Mass Effect and Dead Space.
Nintendo isn't that quite like that. F-Zero needed to have a string of underperforming games before they put it to sleep.