Okay, now that I'm home...
Like I said, the Double Dash system had potential. If I remember correctly, if a character held onto an item then switched, that character still got to keep that item, so it could've lead to a bit of strategy. Also, they could've added a few different modes like every lap you are forced to switch and stay that character, or make character switch points throughout the level, which could've made the party aspect of it a bit more chaotic & interesting. Or hell, like you mentioned, have the Weapons character have the ability to actually aim, which is a great idea. Since they are not driving, give them the ability to actually look around and aim their shells or peels. What they absolutely had to do was make a non co-op racing mode in which you can have a 4 way race. I feel that if you give people options, then it makes it more fun. Like with Smash Bros. Brawl and playing with or without items. Both methods are a lot of fun, but if one was prevalent over the other, that one mode might not be as fun anymore.
However, ultimately what we got wasn't all that well executed at all, and plus again, I hated the handling. Like Fxeni said, the item imbalance was still there and not as bad as in MKWii, but still there nonetheless. I think it had potential, but just did not deliver at all.
And MK64 definitely has bigger races. It's why I love the game so much. The tracks are long, big, and allow more room for success, failure, and pure MK douchebaggery.