I believe the test is an attenuated version of one use in real psychological research, the Vividness of Visual Imagery Questionnaire[1], and has proved to have predictive power. E.g. the scores people give correspond with the level of activity seen in their brains when they undergo MRI scans, so although vague, it isn't "useless" in that sense.

[1] https://en.wikipedia.org/wiki/Vividness_of_Visual_Imagery_Qu...