You wonder why there isn't a name for good dreams but there is one for bad dreams. amirite?

I believe "dream" is the acceptable version of a "good dream" - since the word dream also means "ideal" or "perfect". I clicked NW just be a smart-ass. I admit. I totally get what you mean, haha...but on reflection...no, you're wrong. There is a word for "good dream" - it's dream

Wet dream?

The word derives from the Old English "mare", a mythological demon who torments human beings with frightening dreams.