Depending on the timetable another good field of spots can be reached by foot from Schierke station.
Just follow the small footpath on the forrest side of the tracks opposite the station building towards brocken and you will find some nice open spots to take pictures of the trans running in both directions.
The main shed area in Wernigerode has very good access to observe all the activities, there is a "observation" platform as well as a footbridge to provide elevated visions.
The main workshop in Wernigerode Westerntor is visible from the station's platforms.
As far as I know the HSB even offers guided tours in the works on certain days.
Drei Annen Hohne looks like this with three steam trains meeting there.
Very best Regards,
Urias