Is there a ratio between PDF and Paper pricing of the same item? I'd guesstimate a proper PDF price to be about 60-75% for items under $10 in print, and 35%-60% for items about $10 in print. This is not written in stone.
What price point is too high, no matter the number of the pages (size)? $31.99 is damn high. Not sure if it is too high, but it certainly isnt customer friendly.
Is there a page to price ratio that you, as a consumer, use to evaluate PDF value? 10 cents a page for items under 50 pages, with the cents per page dropping as the product gets longer... there is no exact science
Do certain publishers deserve a premium price for their PDFs? If so, why? I don't really have an answer for this, but some publishers certainly think their PDFs deserve a premium price.
Is FREE a selling point for you, or something the consumer should avoid? Does a $1 price point imply more value then FREE? Why? I enjoy free stuff, and the OSR has lot's of amazing stuff priced for free, so I think free works well.
Does top shelf art add value to a PDF the same way it adds value to a paper product? Art adds to the impulse buy when flipping thru a printed product in a store... PDFs lack that ability, so I'd have to say art is less important for PDFs.
Are lower production values accepted for a PDF product then the same in paper? Probably.
Does finding a PDF product is also available as a Print on Demand product add value to the PDF? How about a PDF / POD Bundle? If something is available in POD, and you get the PDF for free, I'll probably grab the bundle over just getting the PDF alone.
Those are my answers. I have a blog, therefore, I am an expert. NOT!