The same Opera browser was already on the original DS and DS Lite as an optional add-on, I'm not quite sure why people think it's a DSi thing.

The DSi seems too much of a stopgap to be worth bothering with. Games won't be able to depend on any of its extra features without breaking backwards compatibility, so they'll probably just have a few ephemeral novelty features which don't contribute anything to the game.

Even the DSi's WPA support is meaningless because it won't work with current DS games.