While you can change the size of rendered images, it does not look like you can change the resolution of the outputted images in Navisworks.
If you would like this behavior to change, so we have set up the following link is setup for you to submit feature requests, or feedback, directly to our Development group:
http://usa.autodesk.com/adsk/servlet/index?siteID=123112&id=1109794I encourage you to use the feedback link as our Development group is always interested and would like to hear your feedback directly, since you are better suited to state the business case for a feature request.
Chris Aquino
Adoption Marketing Manager | BIM Collaborate Pro
@Aquinotecture