I'm also very interested in this topic Sander and still learning to use VSTi synths. That being said, I ended up getting Arturia's V Collection and extremely happy with their sounds. There's just sooo many synths in this, I get lost in playing (easy to tweak as well).
Anyway when you said 70's Prog, I've been playing around with the Mini V and just love it.....really good if you like the Moog sounds. I have most of the synths you mentioned, but Arturia' stuff is fantastic. Looking forward to getting some good tips on sound design...total newbie here.