Hi Sebastian,
I also have a Tunis Beige, 4 Speed, Early 250SL (RHD) which I have been driving a lot lately. I also have 2 x 280SL's - I have to say I (like most of us) appreciate the early appointments of the early Pagoda's (Extra Chrome, etc). Sadly mine does not have the Gooseneck side mirrors - possibly an error of a previous owner. But I have all the other chrome trims and PS.
Car drives beautifully - especially in manual form.
The anomaly in the values still doesn't make sense to me. I think it is truly is an anomaly. Other marques (E-Type, etc) have higher values for the earlier models that have lower production numbers and are more aesthetically pleasing (like the 250SL).
Do I think it will change and correct itself? - no I don't. MB owners seems to be a fickle bunch and have decreed (probably for good reason) that the 280SL is the 'one to have', and values are likely to stay that way.
Just my opinion of course
FYI - I was first intent on buying a 250SL for the reasons I stated above until a car enthusiast friend of mine said - "the 280SL is the one to have" …..so, like a sheep....I followed (no complaints there). The only reason I eventually bought a 250SL (after the 2 x 280SL's) was because it was a good deal - too good to pass up.