They're a neat idea, but the implementation is... something.
Having them set so you can't buy [halo car] unless you already own one (as a prize) or a significant number of exclusive or sporting cars from the rest of the range would be neat and sufficiently realworldy.
You originally couldn't buy an Enzo unless you had owned an F40 and F50. Ford only sold second-gen GTs to people with a history of fast Ford ownership and a public profile (either through being actually famous or an influencerer). The FXXK Evo, Vulcan, and P1 GTR were all invite-only (although in the McLaren's case you had to own a regular P1 already, which obviously can't apply in GT).
Imagine if in GT7 you had to own (or have owned, thus unlocked on the Collector screen) a Focus ST, a Focus RS, a Mustang GT, and a first-gen GT in order to be invited (in perpetuity, of course) to buy the second-gen GT. It'd lose none of the "special" feeling of owning one that they're going for, while being true-to-life in a sufficiently not annoying way.