Bear in mind that it is a violation of the VectorWorks (and MiniCad) license agreement to "sell" an old version (that, say, has been upgraded). Not trying to be a killjoy here, but them's the facts. I would guess that a lot of what's on EBay is stuff like this.
I would say that anyone who's been with the software for 10 years and has never upgraded is going to find a pretty big change. Such a large amount of change, all in one dose, can be painful, and I empathize. Although working using the same workflows as in MC7 should be possible, it would be a mistake to not make the effort to learn about the improvements over the last 10 years.