These are certainly unique cars IMHO. You certainly know quite a bit about them but for others that don't here is a little background:
The story is the following: In mid '70s, the touring racing in europe (group 3), specified in its rules that the car must have the induction system of the series model sold that year. In '76 the Carrera 3.0 was introduced with the K jetronic. The K jetronic induction system is somewhat limited in ways of tuning so the racers all started complaining that the 3 last years' efforts were lost, and the factory relented and produced these 123 cars with MFI, to satisfy the racers for one additional year.
These cars were specified with non-tinted glass, left side mirror only, manual windows, no electric thermostatic heating, sportseats, less soundproofing, welded in plates for the roll bar on the rear longitudinals, fat rimmed steering wheel, no headlight washers, Bilstein shocks, no sunroof, and no air conditioning unless those options were ordered. There is supposed to be 30 targas, but I have never seen one and neither has anyone else I know. These cars were homolgated for the '76 season so they are designated as 'Carrera RS'. The '74 and '75 Carrera 2.7 models are not RS cars.
Yes I think they should be sold at a premium in the market but the few that I have seen for sale over the years were not offered the premium based on the low volume and Carrera RS status. That might have changed because the G body MFI Carreras have really moved up in value. A good friend in Germany has recently sold 2 very nice examples for around 60k euros each. Your car would be certainly less because the non-matching engine case.
I see you are in Chicago, I am in northwest Indiana. If you want to talk more send me over your phone #. I think these cars are great fun and would like to see yours some time.
