Blues & Twos,
A level D full motion sim is an excellent idea, if you have the money and inclination. A long time ago (when the Tornado TTTE was based at Cottesmore) I had a go in the full motion sim without visuals, it was excellent. I believe that the experience would be one that you would enjoy a lot. As you said it doesn't hold much value for the future you mention but it'll be a lot of fun.
If I had the money I would shout for a trip in a good sim. It'll only knock a dent of a couple of hours out of your real flying but as you say, you'll never get a shot in the heavy metal otherwise.