Coming at this from a legal perspective, does the municipality provide you with any guidance as to what defines a "classic / special interest" car?
Like you mentioned, most jurisdictions simply have a year cut-off (i.e., 25 years or older are deemed "classic"). Without an objective metric like that, it seems like you have to prove that your '87 911 is a "special interest car" while a 1987 Ford Escort isn't. To a government bureaucrat who isn't interested in cars, this might be hard to do.
I think you're headed in the right direction in terms of seeking books and articles, but it may be helpful to zero-in on what exactly you are trying to prove. Also, it may be important to understand how you are going to convey this information to the municipality (e.g., in-person, in writing?).
In any event, I think below are some big bullet points that may be persuasive to those uninterested in cars (disclaimer: this narrative about Porsche is skewed to help you; I don't personally believe everything in the below):
- Porsche wasn't always a luxury sports car manufacturer.
- Porsche used to be a niche, quirky car manufacturer known for its racing pedigree
- Older Porsche cars are known for its raw and visceral driving experience
- In the 90's however, the Porsche sought to expand its market and began building cars for everyday people. These cars are heavier, easier to drive, and more comfortable.
- This pivot by Porsche made it earlier cars more and more special
- My 1987 represents one of the best examples of Porsche's early models, before they changed their design philosophy. It was one of the last hand-built models by Porsche. It is an "air-cooled" engine (like a motorcycle!) that does not have a radiator or require any sort of coolant. The driving experience is raw and direct.
- The market at large has noted the special interest and collect-ability of this car, specifically.
- Nationwide gatherings are held in celebration of Porsche's air-cooled cars. For example,
https://www.hagerty.com/articles-videos/articles/2016/04/12/luftgekuhlt
https://www.hagerty.com/articles-videos/articles/2017/05/08/luftgekuhlt
- As a direct reflection of the strong interest and scarcity of air-cooled Porsche's, the market for such cars has and continues to boom. In fact, values for car models like mine have more than doubled in the past 10 years and are poised to continue growing.
- In light of the significance of this model in the landscape of Porsche's history, coupled with the collectability of this model, I respectfully request that the city recognize this car as a "special-interest" and or "classic" vehicle.
Hope this helps...OK enough procrastinating for me. Cheers and good luck!