Rafa,
Those are nice sets and have historical value. In my opinion they are very collectable but because they aren't official, they don't count as essays.
I collect DDR and all the collectors I know echo the sentiments of those on the website I linked; they aren't considered essays.
I also checked with a collector-friend who specializes in DDR and has on occasion contributed to Michel on DDR stamps. His opinion was less charitable than mine. He throws them away.

A number of those issues have faked expertization marks and are sold to collectors outside of Germany.
If you could obtain a current BPP certification for those issues as essays, I would gladly retract my comments.
Dan
