I am looking for some confirmation.. research or article or otherwise.. that having forms with a whole host of required fields that are not strictly necessary to communicating the data/message the user is trying to submit will turn people off of bothering to submit it. I know there's mention of this in Steve Krug's 'Don't Make Me Think' book, but I'd like something I can link to if possible!
Each case is different, but in general the more required fields you have on a form the higher the likelihood that your user will get frustrated (aka form fatigue).
If you have a specific page you are vetting, i'd recommend doing an A/B test. Variant A has all the required fields, variant B has the minimum set - see which form converts better, then make a decision.