Robert raises an interesting point about trademark infringement. It is true that Porsche only claims trademark rights, among many others, to the term "Porsche Speedster". However, it is important to remember that Porsche does claim trade dress rights to several Porsche models, including the 356, 911 and others.
Trade dress differs from trademark rights, as trade dress primarily refers to a shape or packaging, while trademarks are usually written words. We all remember the distinctive shape of the Coca-Cola soft drink bottle, which is commonly used as the ultimate example of trade dress protection. The U.S. Trademarks Act (1946), popularly called the Lanham Act, is the primary legal vehicle used to bring cases of possible trademark/trade dress infringement, with a large body of case law, both in federal and state courts.
Courts also recognize that those companies claiming infringement of copyrights have obligations themselves to the public at large. The most common defense of laches or acquiescence means that, if a plaintiff waits too long to bring a cause of action against a defendant, he may lose Lanham Act protection status, merely by his delay. The courts' thinking may go something like this: Porsche had the chance in the 1970's to assert their trade dress claims, as replica makers were selling Speedsters on the open market. Now, after so many years, investments have been made, businesses and suppliers and their attendant employees have all secured financing, paid rent and suppliers, all based on the non-enforcement of Porsche. The analogy courts sometime use to show acquiescence or seeming agreement is the "spite fence". You watch your neighbor measure and build a fence between your property and his, knowing that he is building it on your land. You have an obligation to inform him ASAP, not wait until he is done, then claim ownership of the fence.
We all know that Porsche seems to enforce trade name rights vigorously, while seemingly ignoring trade dress protection. Courts would have to determine whether sufficient time has passed for a defendant to put forth the defense of laches, but Speedster replicas have been sold openly for over 40 years, so Porsche may have lost their chance of trade dress enforcement.
At any rate, Porsche and their legal staff will have discussed options for decades, and made decisions based on many factors: economic, good will, public relations, perception, etc. They are not in the least concerned about our discussions on SOC. This is by no means an exhaustive analysis, but may ignite some interest. I always suggest that members do their own research, using several sources, and make a decision based on that research.