"It would have been nice if they'd incorporated a 'before & after' screen so that you could see what it's done"
You don't say what spyder version you bought, but I assume it's a Spyder 3 and this does exactly what you want. A screen comes up after calibration with a clickable before and after calibration. Spyder 2 also as this option.
You can watch a video on the Spyder here
http://www.youtube.com/watch?v=IS9OhkCBUW8http://