As one who catches at a shadow and pursues the wind, so is he who gives heed to dreams: Good News Translation is good here. An alternative model is:

• A person who believes that what they see in dreams is real is like someone who tries to catch shadows or chase the wind.

Quoted with permission from Bullard, Roger A. and Hatton, Howard A. A Handbook on Sirach. (UBS Helps for Translators). New York: UBS, 2008. For this and other handbooks for translators see here.