Is the end of New Super Mario Bros Wii really the end?

Solution 1:

Nope. 5 stars is the maximum. You've really done everything! Congratulations!

Technically, I suppose you could go and buy all the videos now, but you don't get anything from viewing them all.

Solution 2:

Well, there is one thing. You can make the stars on your save file sparkle by never having a Super Guide appear (the green box that rings like a doorbell if you fail to pass a level within 8 attemps). Just not using one doesn't count.

Once even one appears, I believe to earn the sparkly stars you have to start over from the last point you saved, so that the Super Guide appearing isn't part of your save file.

I would probably beat the game as fast as possible. Once you've beaten Bowser, you're able to save your game at any point, not just when you've finished a castle or taken a cannon. This should make restarting a level if the Super Guide appears much less time consuming.