I've just rediscovered your mail and felt inclined to respond honestly, as as a graduate I'm confronted regularly with 'opportunities' to work for free. While I'm not opposed to unpaid work experience, the fact that most of these opportunities fail to point out what valuable experience and other benefits they offer in return for free work apart from an additional line on the CV, makes it difficult not to become a cynic.
The advert mentioned that the role doesn't involve real photographic assistance, and you're describing honestly what it does and does not involve, something that not every employer does these days. Nonetheless it's disappointing to see that someone with a profile like Mr Kander apparently is not willing to pay people to make lunch and keeping the studio patio tidy, all the more in that it doesn't quite fit the picture I have of him and his work. And while I know I would very much enjoy researching projects and certainly learn something (like in every job), it seems to be an assistance role involving general labour and hence I don't see why it shouldn't at least be remunerated with a minimum wage. You probably found someone who is willing to do this in return for travel expenses and being able to say "I've worked for Nadav Kander", but in light of these facts I think few people would still be impressed by that.
Working for free in return for useful experience yes, but not in return for having to prep sandwiches.