That's the factor for me too, I'm simply running outta space, and to choose between having the space for Primus or for the Falcon, I went with Primus.
I bought the Vader and thought it was soso. I don't really get them - despite being a SW and TF fan. I'd want the robot to look more like the characters I think - DV was about the closest in that respect and I *still* didn't like him.
You guys are right, the MF's awesome. Screw the robots which are pretty solid, the ship is nice and heavy. A little thick more more realistic feeling than most other Falcons Finally a toy where I truly appreciate it's electronics