Here’s my two cents.
In my view, the truth is that the peak of popularity for the classic E9 has passed...
Nowadays, very few people are interested in buying an E9 CS or CSi in factory specification.
The market has long since been saturated with factory-spec examples.
Currently, modified examples command higher sale prices.
And, in my opinion, this trend is here to stay for a long time.
If given the choice between an absolutely perfect, pristine E9—complete with gold-zinc plated bolts and factory-original specs (four-speed gearbox, standard suspension, and stock engine)—and one featuring a five-speed transmission, a KW suspension, and an M-spec engine built on an M30 block, most would definitely choose the "resto-spec" over the factory-original.
And they would be willing to pay significantly more for it than for a car in factory specification.
Ultimately, the future of the E9 market will depend precisely on these "resto-spec" builds.