About the Mission Spec course, There was an official mission spec course run out of 427 in Nov/Dec 07. This course was given the green light from 1 Wing. There was candidates from 408, 427 and 403. At the end of the course they were presented the General Aircrew wings from CO 427. Also there was the pilot course in 2005 which produced qualified mission spec's. After the course in 2007 there has not been another official course run. The so called mission spec's over sea's are by name only. "Edit, 430 ran a in house course, not sure of the dates"
There is a lot more that a MS does then just man a DG but that depends upon the mission and how the AC Captain wants to employ them and use the skill set that you bring to the table. Considering MS come from Arm, Inf and Arty with a lot of advance course and many many years of training between them.