Hi Krickard-
Good valid comments by all. Interesting reading.Yes it would be fun to start a thread to showcase these treasures.
I also collect old postcards and think there great. Wendy177 makes a point I think is true about the popularity of Halloween postcards especially the ones with witches.
The answer to your question lies in do you want and have the time to make the money on these yourself or will you pass that opportunity on to somebody else.
From my understanding, if you list them yourself on eBay it shouldn't cost you anything for the 1st 100 each month if you start the biddding at .99 or less so I don't see how you could lose outside of your time,effort,and selling fees.
If you wish to take a hit on the price but make it easier on yourself you can also sell them as a lot on eBay and pass the money making and fun of it all on.
Listing individually would be good and enjoyable experience to learn about these artifacts IMO. Maybe along the way you'll become hooked.
I would suggest that if you decide to list them individually, you include if they are artist signed and if so include artist name, country of origin,subject matter,photo of front and back (sometimes the back has strong selling points),and style (jugenstil,nouveau,deco,ect..) as this is how many of the cards I'm looking for are found.
Even though all your cards will not sell I'd think you'll still be way further ahead money,enjoyment,and education wise if you list individually yourself.JMO
Here's a link from the many who buy these as a lot then turn around and reap the benefits from selling them individually.
http://search.reviews.ebay.com/postcards_Postcards_W0QQucatZ914QQuqtZgGood luck whatever you decide.