Like I said, aa and gradients are just means to an end.
Practicing those in "safe environments" is like practicing to write the word "and" and writing the alphabet up and down for the novel you're planning on writing.
It doesn't really bring you closer to writing that novel just like knowing how to anti alias a perfect circle and how to blend colors to form a gradient won't really bring you closer to an actual piece.
If you describe forms with more than 2 colors, "gradients" automatically happen.
That's not really something you practice on its own.
Practicing anti aliasing on perfect lines and single shapes won't help you if you need to anti alias irregular shapes that interact with each other or if you need to anti alias with colors that aren't perfect blends of each other.
You should draw something.
That would be easier to critique than random lines with a gradient too.
For instance, that baloon. Try to make it look round but only use, say, 10 colors.
