These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Her motivation varies with each version, in some versions, she wants the girl as a servant or an apprentice, in others it is implied that she believes the girl to be equal payment to her stolen herbs (the fact that she names the girl after said herbs helps this notion.) In others, the witch simply wants a daughter. Heck, there are versions where she intentionally creates the garden hoping it will give her the bargain.
One has to wonder if Rapunzel's parents would have really been much of a better alternative considering they were willing to trade her off for some veggies.
Germans Love David Hasselhoff: According to pollings, the story is very popular with American children, even if it rarely adapted into movies or shows.
Nightmare Fuel: "The pretty bird is not sitting in the nest anymore, and it isn`t singing either. The cat fetched it. And now it (the cat) will scratch your eyes out!!" *throws prince into thorn bushes*.
Padding: The Faerie Tale Theatre adaptation of it gives some pretty blatant padding. Half the episode deals with Rapunzel's parents and their craving for the lettuce.