"Rare" is a factor but not everything when it comes to value. A 1969 Corvette with the base 3-speed transmission is rare...the vast, vast majority were built with the upgraded 4-speeds or automatics. They might be rare but have little market value because no one wants them for anything but to modify. Now...a Python with a 2-digit serial number is even more rare and the market value reflects it. A single-digit Python is even more rare and values reflect that.
Cars and guns...not exactly apple-to-apple comparison except in certain circumstances.