The springs just pull off, they're held in place by what appears to be a rubber solution glue. Before you pull them off, paint a mark on the springs (nail varnish is ideal) and take a photograph so you can replace them exactly where they need to go, else you'll be buggering around for hours trying to center the top plate when you put it back together. (1 dab on 1 spring 2 dabs on 2nd spring 3 dabs on 3rd spring then you'll get each one in it's original place and orientation which is the best place to start as they should then only need minor adjusting to get the bonce correct).
If the sets of little grey washers have perished you can buy new ones from http://www.ebay.co.uk/itm/6-NEW-WASH...wAAOSwl9BWKnva
I have damped the top plate with dynamat in all the voids on the underside.
The switches don't just pull off. You have to remove a tiny screw from underneath each switch. You'll need to remove the chassis from the plinth to access the screws.