In your response to Souther, you remark that collectors buy nostalgic items of which they probably could never feel nostalgic. In the use of the term "nostalgic memorabilia", the idea does not necessarily relate to the purchaser or owner of the item.
Many nostalgic items are more iconic items of an era gone by. They are usually representative of a previous generation in terms of style, art, manufacturing, packaging, or what have you depending on the item. And as they say, they just don't make 'me like that anymore.
Since these items are no longer being produced or are in different ways, the nostalgia refers to the people of that era. Many of these items would bring about some sort of nostalgia to someone of their generation upon seeing them.
Show a 12-year-old boy a picture of Rosie the Riveter. You will not get much of a response. Show it to any woman who that poster represented, and you will find quite a different response. That is why it is a nostalgic item.