I do like the Wii's interface, I prefer it to what I've seen of the 360, and anything else I've seen before that.
That said, a few changes could help. Mentioned above is a friend code channel. Imagine a channel you could use to send and receive all of the friend codes of common games you and other Wii owners have, after only sharing the console number? Wouldn't that be something nice? To be honest, I think a lot of us expected this feature, which was only partially satisfied with Mario Kart, sort of.
After that, I'd like to have a grid of channel pages, just to allow more. a 3x3 section would be nice, I've filled mine with VC games, and I'd (naturally) like more space. Alternatively, if there were channels based on consoles, that would work, as well.
A feature I enjoy is that channels can actively update what information they show when you're connected to the net. Take a look at the channel for weather, or My Nintendo Channel, or whatever they may be called. That's a nifty thing to have if I've known one.