OK, 6 switches done. Quite boring to define 30 DCI images (so far) without templates.
Also, I found no way to add a map legend for the different state icons because decoration images can have no text. The only way I found so far is to create a dummy condition with the icon as map appearence and the key intop the name field. Setting propagation status to always "Normal" and then place it onto the map and unmange it (as the grey "X" is less disturbing then the blue "?")
The two last switches are Netgear switches which have no standard MIOB for STP, I will have to retrieve the private one.
I am quite happy with the result.
Thanks again for having pointed me into the right direction.