Interesting numbers on Hagerty's website for 2800cs values versus 3.0cs values.
1969 2800cs - Good condition: $15,300
https://www.hagerty.com/apps/valuationtools/1969-BMW-2800CS
1973 3.0cs - Good condition: $40,300
https://www.hagerty.com/apps/valuationtools/1973-BMW-3.0CS
1969 2800cs - Good condition: $15,300
https://www.hagerty.com/apps/valuationtools/1969-BMW-2800CS
1973 3.0cs - Good condition: $40,300
https://www.hagerty.com/apps/valuationtools/1973-BMW-3.0CS