I would guess there is a much smaller market for memorabilia in retro computing as there is for hardware - Things you can use your flag for are somewhat limited - A piece of (working) hardware promises basically unlimited fun. On the other hand, non-hardware stuff has generally much earlier met the dustbin than real hardware, so it should be considerably more rare.
Price for non-hardware stuff is definitely much more based on meeting the right buyer in the right buying mood at the right time. I, for example, have a quite decent retro collection, but have never thought (and don't think I ever will) of spending money on anything else but hardware. Just blatantly assuming everyone else might be like me, I'd say the typical retro computing guy will consider such memorabilia a nice side dish, but not the main course he would be spending considerable money on. You are searching for an Apple memorabilia collector, not a retro computing hobbyist.
In case you want to sell - I guess neither eBay nor auction houses would be the right place - Material like your example are too rare and too specialized for selling through generic channels IMHO (It definitively doesn't hurt looking, but don't have high hopes to get real guidance from there). Better try and ask in specialized Apple retro forums - a lot of them have "for sale" areas - whether someone would be interested to buy and what they would be willing to spend. I guess the proposal to try and contact the original manufacturer is a very useful one as well.