It really seems to be a law of nature that people tend to grow out of the available storage space however much they may have available.
Buyers looking for their first home come from apartments, and often-small rental homes where their storage space was severely limited. Those looking to trade up often do so because of an increase in family size: they, too are space conscious.
Whatever the situation, the closets and storage areas of your home are sure to receive close scrutiny during a showing. Accordingly, you should do your best to see that they are kept uncluttered and don't appear too crowded.
You need to capitalize on what you have and the best way to do it is for these spaces appear to be more than you need, not less. You will likely have numerous items that you won't want to take with you when you move, so holding that planned garage sale before you list the property will help in this regard.
You may even want to find temporary space elsewhere for items you need to retain