From what I've seen/heard IRL, I'd say it has the worst word of mouth by a long shot

That's anecdotal. Wii's sales in the first few years, though, aren't. Unless you claim that dozens of millions of people heard bad things about the console that was a huge phenomenon and still bought it, which is silly and desperately trying to argue against the evidence.

Your right, it was a huge phenomenon. People were going mad to buy them because it was the 'in' thing to do at the time and so they could experience motion controls. That doesn't change the fact that once the people bought it they may have seldomly used it and regretted buying it once the novelty wore off.

It should be called NES again.

But then again, having "Wii" in the tittle, ensures at least 20 Million units just because.

My solution would have been to come up with fresh and exciting new name that differentiates the system from the Wii (in order to further solidify the idea that the Wii U is for core gamers). Nintendo Revolution for example.

In order to make sure the casuals are not confused I would put a sticker on the box for the first year or so of its console life that says something to the effect "Play your Nintendo Wii games and use your Wii remotes/accessories on Nintendo Revolution!"

This seems like the best of both worlds to me. You get a new name so Nintendo gets some level of credibility in their attempt to grab the core gamers, and casuals should, for the most part at least, realize that the system is a successor to the Wii, and they can use their old Wii stuff on it (Nintendo's been really awesome when it comes to backwards compatitibility in the last decade so it would advertise this selling point as well).

Considering that it was a huge phenomenon starting late 2006, don't you think this word of mouth that it's only fun for a week then gathers dust would've spread before it sold as much as it did in the next few years?
Regardless, your hypothesis is based entirely on your personal experience, which means nil, really, since, as I stated, my experience is the complete opposite. There's absolutely zero meaningful evidence that any non-hardcore gamer got bored of the Wii.

Anecdotal evidence is not the best argument to judge an entery installbase.

Of course they should have dropped the Wii name from their upcoming home console.

In fact, I have been asking myself every day since the initial Wii U reveal why on Earth they would decide to stick to a brand name that ensures over a dozen million units of sales. It makes no sense at all.

I know people who did have regrets about buying the WIi and Rock Band and im not talking the core audience, either. Not saying that there is alot, but you cant say everyone was satisfied. 

Of course, but that goes for virtually every system and game.  I regretted all my 360 game purchases, but that was just me, they sold fine and had successful sequels so obviously most everyone was satisfied.   But Wii and Rock Band were more 'fad'ish, I'll give you that.