as I'm a strong believer that if you're looking to invest, you should look at the stock market, real estates etc etc. Watches are meant to be a luxury item that enriches your life.
Having said that, as other pointed out earlier, the 317K is unique as there're only 500 of them w/ true PVD'ed movements and I doubt OP would continue producting 317, even w/ the smoke caseback crystal configuration, in their serial production for long. So all and all, the 317K would simply prove to be a small subset of an already limited range.
As Yves mentioned earlier, speak to your heart and follow your instinct!