I was actually thinking this as well a while ago, haven't tested it much yet though.

While daydreaming just practice being aware that you're daydreaming, it's not as easy as it sounds because just like in night time dreams we tend to drift away during daydreams, so I do actually think it's really good practice!

Also visualisations get stronger and more detailed the calmer the mind; for example I can visualise in a lot better in the middle of meditation, or even if you just sit quietly and daydream the visualisation grow much stronger after some time when you start forgetting about the outside world. This is also good for thinking up art / design / problem solving / anything else, you have to sit down, relax and let the mind concentrate.