Personally, I've not seen GO Mustang's selling for anything more or less than a red Mustang. GO can be harder to sell actually because the color isn't a popular one outside of the specific few fanatics.
I'd say sell the damned car. The moment you become so emotionally attached to a car like this that you've only owned for a couple of years is the moment you should hear the money falling out of your wallet. If it sits, not only does it depreciate, but unless it is driven weekly, NOT monthly or bi-monthly or bi-annually etc...but weekly, you will very likely end up with spiders, roaches and other bug infestations. You will also have dry rotted rubber every where, seals will be trashed in no time once you start driving it and like a Boat, you will be throwing money at the damned thing left and right and in the end, you'll just be highly pissed at yourself you didn't just get rid of it in the first place.
If you were going to sit it up for the next 30 years and try to sell it for more than you bought it for, I could understand going that route. Barely since fuels will be changing so much over the next three decades, but you aren't. You're talking three to four years. If you don't have a highly trusted family member to take care of it, sell the fucking car and get over your emotional attachment to it. You get to Germany and buy a $5,000 Benz or BMW and you'll fall in love with it since they are setup so much differently than American cars. They are built for speed, cornering and having FUN! Not many $5,000 used cars you can buy here in the States that would bring a grin to your face like one in Germany will.
You try to sell it over there, as mentioned, and just the environmental changes that are needed for the car, plus the safety upgrades, (you will be instructed to remove the large majority of your aftermarket parts to pass inspection on that side), plus the noise restrictions, the cost of fuel if you run out of gas allowances on post or you're traveling in it. The cons far out weigh the pros in this one. Sell it, save the damned money and buy that special, really historical car you want when you return.