If the wonderfull 101 can have a far lower WW launch week and still end up sellink 500k, so can kirby. except that in kirby's case, it will be profitable.

Thanks^ Also What makes you thinkthose are unimpressive sales? You want to know why they are not unimpressive? Because they keep making them. Outside of Mario Spin offs + Pokemon, its one of the only Nintendo franchises that actually has 4-5+ entrys per generation. 

Basically inputting that nintendo are happy with the sales otherwise they wouldn't keep putting Kirby in the spotlight. A good example of this is DK. DK Returns was a huge success and of course a sequel came out very soon after (on wiiu) even before metroid.

As for popularity, he certainly hasnt declined, not going by Triple Deluxe a game that i think is at 1.7mil+ by Dec 2014 and will likely be above 2.2mil-2.3mil lifetime. BTW that is actually one of the highest selling Kirby's as it usually is a 1.2mil-1.5mil seller (at least traditional and big spin offs)

I think part of the reason why it hasn't so well so far is the fact that it looks super childish. I love the aesthetic, clay Kirby is super cute and the whole game is visually stunning, but I doubt that a 10 year old boy nowadays would want to be caught dead playing it. Let alone a 15 year old boy(I'm using males here because its still the primary gaming audience). I grew up with Kirby and still caught shit for liking the little pink puff ball. I always loved all the different powers and different ways you could tackle each enemy and level. I thought it was pretty neat, and to be honest, I thought Kirby was a bit of a badass. What other Nintendo character could cut you, stab you, light you on fire, encase you in ice, stick you in a whirlwind, electrocute you, then just blow your ass up all while dodging apples?
I also think that a huge part of it was the gameplay choice. If there's one thing people generally don't like, its the loss of control of their character. Sure you guide Kirby with lines, but you don't actually move him. Not to mention that Kirby is know for the different powers, simple platforming, interesting level design, and fun gameplay. Some of that exists in Rainbow Curse, but the focus on a variety of powers is absent, the level design is decent, and the gameplay isn't very fun when you have an HD Kirby game you have to play on the gamepad exclusively.
I honestly think that Kirby is kind of a perfect storm of what gamer's just don't want anymore. It makes me sad to admit it, but its true. I think it might have sold better if it were a more traditional Kirby game. Even then, the little pink power puff needs a bit of an overhaul. Maybe a 3D environment instead of the traditional 2D. Something similar to Starfox Adventures(Yes, that game is awesome even tho it isn't traditional space combat).

I look forward to getting this someday... when I have money... It might be one of the last Wii U games I do get because of the weak Canadian dollar.

Journey has better graphics, better art style, better music, and I bet it is a better game as well. I paid 15$ for it. So yeah....

Then every  game with worse art style, worse music and worse as a game than Journey is overpriced if it´s above 15$.... i guess the 75% of  games  are overpriced nowadays then. 

Kirby RC is better than the vast majority of games released this days at 60$

So no, I don´t see it overpriced.

I think that is a major issue for Nintendo.  They stick with the same old games for far too long. Meanwhile other publishers move on and create fresh new IP'S. 

Like Splatoon? Or Like Animal Crossing? Or like Xenoblade? Or like Rythym Paradise? Or like Codename Steam?

Don't forget Tomodachi Life, Steel Diver and Wonderful 101. Hahaha

You gotta love ignorance

A few shallows don't make a summer.  

My point is many publishers could keep many series going if they only wanted to match these numbers.  They move onto bigger and better things.