Chris, I am happy that you enjoyed our little but friendly country.
It is true that the Mercedes population has been dropping in the last few years. If you wondered around San Josť in the middle of the 80's, you could not believe the inmense number of M-Bs that popped everywhere.
Although car taxes are extremely high in this country (reason because there are not to many M-Bs), at that time used car importers found a loop hole on the tax law and began importing 5 year old cars like crazy.
Later the demand dropped and the government raised the taxes on used cars.
Still, Costa Rica is one of the few countries in Latin America where once in while you can see a S600/C32/E55/G55/SL500... going by. In upscale suburbs you can see C/E/S and G classes in good numbers.
CL 500, 1998
S 500 L, 1998
E 320 T, 1995