GBA Connectivity: Ingenuity or Gadget Gimmick?

For those of you who have no idea of what I'm speaking, I'll give a brief explanation: One of the biggest features that Nintendo is pushing with their products is GBA/Gamecube connectivity. In the simplest terms I can muster, I'm talking about the ability to connect a Gameboy Advance to a Gamecube console like a secondary controller via a special link cable designed specifically for this purpose.

There are a lot of Gamecube games that have taken advantage of this feature, which happens to be entirely exclusive to Nintendo's product line. Examples include Animal Crossing (where the player can download original NES games to their GBA and play them on the handheld, as well as a ton of other extras), The Wind Waker (where a second player can control the character Tingle as a sort of sidekick, using the GBA screen as their visual reference and menu system) and Splinter Cell (where the GBA becomes a sort of overhead scanner that can give an infra-red image of the level from the top down). These functions are all really quite enjoyable, and enhance the gameplay to an extent.

But how much? In my personal opinion, I think the connectivity issue could produce some really great concepts and gameplay experiences. But, when are those connectivity revelations coming? Will there be some all-encompassing feature that changes console gaming entirely, or have we already seen basically everything that can be done with this feature?

In other words, is GBA connectivity a possible burst of design genius, or is it a gimmick? Will Nintendo be the only company to travel this path, or will the PSP feature connectivity capabilities as well? Will this feature thrive and continue to be seen for years and years to come, or will it die when the Gamecube's lifespan has come to a halt? Discuss.