What a shame that the rest of the network is closed for engineering work from 4-29 November, otherwise you could have got halfway to Ilmenau by steam - as it is, Eisfelder Talmuehle is sadly off!
Rather than the 3-day ticket, I'd suggest the HarzTourCard
http://www.nasa.de/index.php?id=66, which for EUR18.- gives you 3 days unlimited travel as far as Schierke, plus local buses across the Harz (on the Sunday it would take you to Hasselfelde for a connecting bus to Berga on the Halle-Nordhausen line - the bit I've done is a pleasant ride).
BTW Schierke-Brocken is still EUR 32.-
You can buy the ticket at the HSB booking office or (I think) the tourist office, but it's still not very well known. This is also valid on the Halberstadt trams, which have a tram/rail crossing and on Sundays only potter down the decrepit rural section to Klus - though they now use new trams normally. 2 hours between trains in HBS should do it (there were lockers at the station when I did this a few years back)
Back to the Brocken: the only time I did the trip - starting from Erfurt behind a class 232 (well it was 1996!) - the weather changed dramatically while I was there, from mist and rain to cold and clear (you could easily see as far as the Thueringer Wald), so don't be put off by November weather, unless it's really awful (in which case just use your HarzTourCard). Of course the proper way up the Brocken is on foot, like Goethe!
Enjoy St Martin's Eve too (I think we've had this conversation?)