I just finished pre-ordering both packs for a cool $12! My first ever pre-ordered DLC. Hell, I think it might be my first purchased DLC ever.
When I heard about the DLC yesterday, it made me very happy. As you can probably tell, not much DLC interests me, but if it's for some of the awesome games that Nintendo releases only once per console generation, you can likely go ahead and sign me up. Let's face it, we probably won't see a new Mario Kart game for at least another four years, so I'd love to see this one kept fresh with updates! I imagine Smash Bros. may get a similar treatment, which I also welcome.
I don't see this as DLC that should have been included with the game in the first place. The original game was fairly fully-featured, including 30 characters (though granted, several are similar to each other), and the standard 16 new tracks and 16 retro tracks. With the new DLC bundle, I'm getting 16 more tracks across 4 cups, 6 new characters, and 8 new karts. To me, that's a great deal! I'm paying less than 1/4 of the original retail price for what is essentially half of a game! And that averages to less than $1 per track!
In case you can't tell, I am looking forward to this.