The upgrade of the PS+ DriveClub version is a DLC-pack. It's not that unusual that you can't play the bought/activated DLCs anymore when you lose access to the main game (for example if you sold the disc with the main game). The only differences are that the main game has an expiry date and the unusual proportion between main game and DLC... usually there is way more content in the main game than in the DLC(s).
That said, Sony shouldn't go this path... the "upgrade option" is too similar to their test versions of full games with an unlock option. Or at least they have to make it absolutely clear to any buyer, that the access to the game and the DLC ends when the PS+ subscription expires. When someone tries to buy the additional content, a straightforward requester should pop up: "Do you want to buy the full version for $ x (no expiry date) or the DLC-upgrade (expires with PS+ subscription)?"
