25 year rule in USA is a criminal law paid for Mercedes, which means that any non compliant car imported into USA must be at least 25 years old. Supposedly you are allowed a to import them for show and off-road use but federal government refuses to allow rare Japanese race cars. The 60 something head of the revenant government agency hates Japanese cars and refuses to allow any rare JDM car saying they are "full of computers and junk". Recently the prices have been exploding because many coveted cars are hitting the 25 year mark. Plus with many illegal import methods or people just storing them in Japan waiting for 25 year mark to hit. Growing prices and big interest can prove to be a great investment vs boring 401k's with crappy returns.
take a look at Silvias