That might have been a good item to include with the sale of an older Mac that could boot to that system...
Same thing that I do when I occasionally sell an older Mac - usually include one or two old OS X installers that would work with that Mac model.
but, if you just have a couple of "orphan" system DVDs, and you think it's unlikely that you would ever use those DVDs for anything other than a drink coaster, then eBay (or a convenient recycle bin) is a reasonable choice.