Thanks for the suggestions.
The process is a bit slow as I am only able to do the work when I am at my parents' place which is on the other side of the country. I'm there about once a month for work and am busy scanning things in the evening.
The collection will not be leaving our hands, that is for sure. The cards have already proved to be very useful to my work. A relative obtained a transcribed copy of my g-g-grandparents' marriage certificate from the archdiocese in Paderborn, Germany. It listed the bride and groom's parents with place of residence and the womens' maiden names so I thought we'd solved the mystery of that generation. Then I look at a funeral card for one of the women (g-g-g-grandmother I had presumed) and it seems that there might be an transcription error in the marriage certificate, an error on the funeral card, or possibly a second marriage to a woman with the same first name! A new mystery to solve.
Interestingly, in the same package I found the will of my great-grandfather's brother who returned to Germany. I think everyone in the family assumed it was just a family letter. I'm the only one who can read and speak any German and realized what it was and couldn't wait to tell my parents. I scanned that document immediately, needless to say.