Can whimsical be good?
In nature the most obvious example of whimsical, must be the butterfly. The butterfly has four stages of development that could point towards an aspect of the positive side of whimsical; the eggs become larvae, that pupate before the butterfly one day appears.

These four stages can be compared with the four stages of development explained by the psychologist Carl Gustav Jung. First we are busy with how we appear (body, looks and cloths) then we are busy with what we achieve (car, house, spouse and position), then we want to give and leave something behind us that transcends the physical values and finally we awake with spiritual awareness. (you can read more about the butterfly and Jung’s stages here).
Also, in homeopathy the experiments with butterflies have shown that people that need butterfly remedies can appear whimsical, lost, confused, without direction in life or stuck and not able to go through a metamorphosis (read more here).
The butterfly cures with giving a new perspective; rather than changing the path they perceive it with understanding of its wise and carrying necessity. They lift you to a broader perspective, a higher holonity, a bigger overview or more spiritual stance.
Just to see or experience this makes you see whimsical differently. There is a possibility of a good whimsical indeed.
If you want to learn the different archetypical aspects of whimsical read here.
Let me finish this with a little poem called; Flowerfly.

Flowerfly
Fly fly flower, fly
let your body die
Free yourself, float in the air
Fly here, there and everywhere
Flight of fancy
Fluffy
Feather light
Feel free, free, free….
Fly fly butterfly