While there may not be an exact way to gage the full response (in amount of downloads) to your uploads you should rest assured that if you post to relevant target groups that have activity there will be people that are very grateful.
Usenet is a big source and with the many groups and users and language barriers out there it would be impossible to know how many are downloading your particular upload. Not everyone that uses usenet use indexes or forums for nzbs, many still grab headers and even then some still prefer to not give a thanks and just 'hit and run' so to speak. But this is one of the good things about usenet...Anonymity.
But do rest assured that if you are posting to the proper group(s) there are many who are grateful even if it is not shown on an nzb download counter :yup: