You bring up some good points, as I have suggested we should have a seperate Explore standalone without needing to download Platform Builder, but if you look at programs like Kodu and things like that, they don't have a separate thing for their own "explore" section. They just don't. While it might be useful here, it's not that big-a-deal.
I'm not nessecarily against fangames, but I think that we should be careful. I myself wouldn't use official sprites unless it was just a personal thing, or small demo or something like that. But if someone else wants to use custom sprites, that's their buisness. Not mine.