I see value in GDs comments. He had the Loyale/GL platform at one time and he decided to move away from it for the reasons he states. His reasons are valid. But they are equally valid reasons to not buy and maintain any old machine. With a car that ceased production in 1994 the lack of specific parts may be a good reason to stay away. But, as to the value, the market is the market. It seems like many of these are coming in under $1,000 but ones that are not rotten and seem to have been well maintained are going for higher prices.
Some people are sticking with this GL/Loyale and keeping them running. I liked driving the one I did. My sense from talking with the owner was that he was able to find parts when he needed them or make due with substitutes. There are many aspects of the simplicity of the GL/Loyale that appeals to me. I do need to admit that I fly a 1946 Piper J-3. Low power, slow, uncomfortable, etc. Sometimes tricky to find parts for and maintain. Sometimes when flying about 1000 ft AGL I fly along a freeway so the movement of my shadow can be compared to the speed of the traffic. I need a tailwind to move faster then the cars. So why maintain and fly this plane? In the past I have owned a 59 MGA, a 64 Porsche, a 65 Beetle and a 64 Corvair and a 73 Austin Mini. I rode a Yamaha XS650. All quirky rides. My daily drive today is a Toyota. There are members on the forum who like the GL/Loyale and are driving and maintaining them.