It's probably safe to say that a majority of the system memory, and that includes the GDDR space of course, will be used for graphics assets, but that applies to all consoles, not just the Wii. Better textures und more detailed models always make a difference and hence are a good way to use up the available memory.
It probably isn't a huge problem either way. Flipper has edram for the framebuffer and an enormous texture virtual memory kinda thing/cache so it can cope with poorly performing external memory really well. Hollywood should have inherited that ability.
I have absolutely no doubt that all of it will be available to native Wii games. As you say, it would be a waste. Also because the GDDR alone would be just too slow for a new console, even for Nintendo's humble standards.