I suppose since Spoilers and Persuaders are not on the current price list it may contribute to the perception of rarity. You're free to order a dozen Spoilers today, so it's not like they are exactly discontinued.
Prices are always what people are willing to wait for and what others are willing to shell out. It's extra tricky on a product like ours since each one is unique - even the black finish. Though in the 1980s we made a LOT of Spoilers and Distillates in Jet Black (and many with Exploiter body shapes), most with chrome plated hardware.