Germany: Stamps On Presentation Cards

I have a number of these from the time that I did business with Deutsche Telekom and Deutsche Post.

Do these cards have any intrinsic value over and above the value of the stamps or would I be better trying to sell the stamps individually, or cut from the cards with their postmarks. Here are a couple of examples:





I have the same question regarding Christmas cards received from my contacts. Here is an example:

These are collected in Europe, or at least thy used to be. I would lave them the way they are.

Peter

Thanks, Peter. That would have been my first guess.

Frank.