This reminds me of long discussions about the monetary value of herbarium specimens on the Herbaria Listserve many years ago. We hated to find such a value because the specimens become historical artifacts that cannot be replaced. Putting a dollar value on any but the most recent and replaceable ones is unrealistic. We can’t buy additional specimens from the Lewis & Clark Expedition, for example.
Nonetheless, there were three major reasons to do this. First, people who donate to herbaria want a dollar value for tax deductions (at least in the U.S. tax system). Being able to take a deduction increases the likelihood that the specimens will be donated rather than sold, so this is good. Second, though I never would have expected this, herbarium specimens are sometimes sold on the open market, usually for interior decorating. This is disturbing not only because the more attractive ones are usually lost as scientific data but also because the less attractive ones are likely to be trashed. Third, institutions may need to know the value of their holdings, partly to justify, for example, a university spending money on a herbarium (It’s so valuable!) and partly for insurance purposes. Of course, that can kind of backfire – a major Australian collection determined a dollar value for the collection and found out they couldn’t afford to insure it.
We debated matters of rarity and of historical value, of hiring people to collect, of expeditions to interesting places, of modern donations, of competing in the market place for a historical collection being sold for home furnishings. We ended up deciding that we could justify $10 per specimen for anything (e.g. most donations) and that special situations might change that. This was thirty years ago, so one could justify more now, I’m sure.
Monetary value of iNaturalist observations would be much, much lower, for several reasons. First, digital photography and uploading go so fast that even if one assumed a high pay rate, one probably couldn’t justify 10 cents per observation. Second, whatever market there is for the observations as photos concerns the observers, who retain copyright if the observations aren’t just open for free. Third, iNaturalist doesn’t charge for the data, so no monetary scale there.
Of course, economic value isn’t just what we could put down on tax forms. It’s also the effect the observations have on land prices, education, conservation and therefore reducing pollution, etc. That’s hard to calculate. What could almost be calculated is what iNaturalist saves researchers and land managers because they can get data without paying someone to go out and collect it. All in all, this is a difficult question.