One of the first things I would do is get a better understanding of is usage. What is the information that is being entered going to be used for? A good sense of what is important and what is not will quickly come from that. This will help you take your first cut with all the data fields. When in doubt, leave the questionable fields in.
Then, take your new short list and group like elements through an affinity exercise, using sticky notes. Have two or three different groups do it. Any fields that don't naturally "fit" become candidates for removal.
Next, mock up a restructured data entry page in a way that you can test it, using the affinity data to group "like" fields, using the affinity take it tote people doing their work together their reaction. Having them actually USE a new version of a form will prompt a much different and frequently more specific feedback than looking at the information in an abstract way.
Finally, be clear about what the goal of the redesign is. Is it to increase efficiency for the person doing the data entry? Is it to ensure that the right information is being captured? Clarity around what you are trying to do can guide you when it comes to keeping or leaving some fields.