Considering if successful (and it looks like it is) Nintendo can now probably make Splatoon games/merchandise/etc. for the next 20 years ... I'd say it was worth it. 

Gotta spend money to make money. 

I was in Japan as the game was releasing by the way, I saw Splatoon ads on TV a couple of times and once on the subway (some of their subway trains have LCD screens that run commercials alongside train info). But nothing super unusual. I saw multiple TV ads for The Witcher III as well. 

$8 million dollars ... lol, is a drop in the bucket. Major movies have marketing budgets of like $100-$150 million dollars. 

Well, Reggie did say that Nintendo's long term goal for Splatoon was for it to become for shooters what Mario Kart is for racers, (and what Smash Bros. is for the fighting genre for that matter).
If they keep up this momentum, I think that will definitely be the case sooner rather than later.

Animal Crossing: Happy Home Designer for 3DS. It's a spinoff, and was revealed in a Direct earlier this year.

Currently no news on a Wii U Animal Crossing but 3DS is getting Happy Home Designer which is a spinoff which has u play as an interior designer and is the first game to utilize the new Amiibo cards.

Gods, I almost couldn't have been more right with my Splatoon 2nd week drop. I said I expected a 50% drop and it is a 54% drop. That relatively light drop should secure good legs long term. 300K should be a lock. Maybe even 400K.

But what's with the gravity defying feat of Wii U hardware. It is against the laws of physics for the hardware to go up in the second week of a significant game release. Has there been bundling or price specials or something. No way is Wii U up just because of normal Splatoon sales.

I don't think there is anything else worth commenting on.

Splatoon will sell 700-800k lifetime in Japan.

I think that's being overly optimistic and placing too much of a sales expectation burden on this game. People gotta calm down with their excitement.

Nope.

Sorry, but the Splatoon hype train is too strong. Splatoon in Japan will easy pass the 300k mark by end of June, and then, 400k to 500k by end of year.

After that, with a good legs, 700k / 800k seem very possible. People have already underestimate this game so much, so, why be conservate?

Splatoon already proved that anything people should be even more optimistic. Already passed 300k mark (with digital, there is a tbone's thread somewhere with the numbers)

500K by the end of the year means pretty much the end of the line. It ain't goinna do another 200-300K selling at 1000 units a week, which is where it will be selling at at the beginning of next year. It'll be below 2k/week within a couple of months.

Beating low expectations, and becomming the 3rd or 4th best selling Wii U game ever in Japan are not the same thing. And the first thing certainly does not assure the second.