Hope you have a Gamecube component cable. All GBA games on the Gameboy Player are 480p when using it.
Do the games look that much better if they're in 480p vs whatever my composite cable produces? What is their resolution anyway?

On topic, the Gamecube did do well, in that Nintendo made money on it. It didn't outsell it's competition (if that's what 'not doing well means') because they had no way to market it much past young kids and the Nintendo fans.

The reason Wii took off is because they figured out how to increase their potential market by focusing on their strength (kids and families and Nintendo fans).

I'm not sure what to think about the DVD argument personally. My first leanings were that it wouldn't matter much, but perhaps marketing towards the family looking to get their first player and at the same time showing them they can also buy games for Sally and Steve to play on, that might've gone somewhere.