If CLASSIC = Monetary Value then,
Besides Quality and Condition, Rarity has EVERYTHING to do with value when dealing with Antiques. There are virtually collectors for everything under the sun. Furniture, Art, Toys, Baseball cards, Matches, etc. the list is endless. when you have these obessive collectors vying for something that is in severe limited quanity, Price will go up to reach the equilibrium. With a limited quantity of product, Demand goes up = Price goes up. The product holder for the rare item gets to pick his price because it cannot be had anywhere else. less sellers produce less compeitition.
Obviously there are different variables that effect price as well. Political influences during the time of the release of the product, Age of the product, Historical significance, and so on. But utimately all these different variables ultiimately effect the rarity of the product. For example, a 17th centry musket has a high value because mainly it's rare because its old, has historical significance, and is high quality.
Who said that "Classic = Monetary value"???? I find that totally oversimplified, and false at face value.
Monetary value is the sum of MANY factors, classic status being just one of the many, as you pointed out later in your post. The early VW Beetle, the Ford Model T and A, the 64 1/2 Mustang, are all classics by any measure, and all relatively inexpensive to buy.
Secondly, rarity does not have "everything" to do with value. A 1972 AMC Matador is probably a rarer vehicle on the face of the earth today than a Hemi Cuda. So "rare", all by itself, means zero. Rare only works when it's the kind of rare YOU WANT. I'm always laughing at ads that brag "rare bench seat", or "rare straight-6-cylinder SS Impala" (you actually could get a 6-banger SS Impala in 1964) trying to squeeze a buck out of the word "rare", when it's the actual rareness of the car that makes people walk the other way. Or the Medium Lime Mustang with brown vinyl roof and vermillion interior, 6-cylinder 3-speed, with 8-track and dog-dish hubcaps, with the Marti Report framed and displayed on the dash proudly stating "ONE OF ONE MADE!!". Wow, that's rare. Must be a CLASSIC! MUST BE WORTH A FORTUNE!! LOL.... Classic applies to such a wide variety of stuff, you can't set standards based on just rarity, or just value, you can't be so simplistic. There's always an example out there that will shoot a big hole in your standard. Look how much dough people are blowing on top-restored 55-57 Chevys these days. When new, they were the common man's car, mass-produced, and cheap. Today the well-restored ones bring $40-$80K depending on bodystyle and options. Twice the money that it would take to buy an equally well-restored, and much rarer, and much fancier/high quality, 55-57 Caddy or Olds. So classic has less to do with rarity, or quality, or performance, and more to do with emotion, heart, and heritage, which the lowly little Mustang, IN ANY TRIM, has in abundance.