While the only help I could possibly provide is a long-ago photo of me in my Ghia L6.4 in the early 1980s, I sold it within weeks of buying the car and have little info, but I might be able to find the VIN for the car if the file still exists. I know it was not in Europe back in the 1960s.
I find it interesting to look at what is parked in that lot. Next to the Ghia we find the back end of a Mercedes with CD and PL markings [CD for Corps Diplomat]. I find it interesting the Polish diplomatic car would be a German car, not Polish or other eastern European car. Above the roof of the Ghia I think is a circa 1962 to '64 Chevrolet sedan. Next to that is a tall Vanden Plas Princess limousine, a typical limo used by the British Ambassador. Next to the Princess is a GAZ13 Chaika limousine. Off to the extreme right I think I can identify a ZIL limousine [or 2] as well.
The grand opening of any eastern European State Opera is an opportunity for Politicians and Diplomats to mingle on the premise of the arts, not politics. If this was in a western European situation, we would see elite cars from business leaders as well, but this is Warsaw, so I would expect most of the cars in this lot are for diplomatic or political use. The license plate on the front of the Ghia is indeed small like Swiss or Italian plates. I would suggest you might focus on who in the Swiss and Italian Diplomatic community might have owned such a car. My money is on Swiss ownership.
But there is another component to this photo and the Ghia. It's winter. The ground, roadways, and parking lot are covered in ice, snow, and slush. Many of the cars are dirty, some have snow on them. ONLY the Ghia looks as it did when new. Not a single drop of water/dirt/slush is to be seen on the car, not even the tires are dirty. Nor are there boot tracks around the car from a chauffeur wiping the car down. The only other photos where I see snow/slush/ice on the ground and elsewhere, without human tracks or tire tracks visible, while the feature vehicle is clean and dry, are for auto manufacturer's PUBLICITY PHOTOS.
Because this car is so unnaturally immaculate, with no evidence it was cleaned after being parked, I suspect the car was placed in position in advance of a real event, the car was parked & covered hours before, perhaps for a possible European Ghia L6.4 brochure or media package. And yes, auto manufacturer's publicity departments arranged photo shoots like that on a regular basis.
