Sorry--posted in a rush, and should have specified I'd checked Ebay. There just aren't enough lots on there to get a good average, so I wanted to check if there was a general consensus, but it sounds like there isn't, so I'll go with what tailrustedtealeaf said. Thank you so much!
BTW, unless I've missed something, these German babies didn't come with much in the way of accessories originally... I thought it was just a bottle that wasn't any different to the ones available in US/UK. So adding accessories *shouldn't* increase their value by very much.
Don't worry, I will be listing my collection in the For Sales forum, once I've got everything organised!