I think if this update consists of 3 new cars and a couple of new races then it's safe to say it's a dissapointing update. But I think most (if not all) players are yet to acquire all of the cars in GT7, it would make sense to me that new cars at this point aren't what the game needs as a prioirty.
New track layouts were previousely mentioned, and would be nice, but again, probably not what the game needs most. Although I'm not an online gamer at all, it seems the online portion of the game needs major work. In addition the offline portion is severly lacking in end game content (if you can even call it end game when there are no races for the games fastest cars).
It needs at least a dozen + new World Circuits events, not missions, proper repeatable events, races and championships. And that's just to get the updates to the single player properly started, this should be followed up with further updates adding to the world circuits significantly. Missions, Menus and other challenges can also be added as well, sure, but they must improve the World Circuits significantly and significantly increasing the payouts for Custom Races would be nice.
I get maybe they didn't want someone to buy their first car and earn 150k Cr for 5 laps somewhere in a custom race, so maybe the Custom Race prize Cr should be tied to your Menu completion or collector level or something.
If they add more than a dozen new races, with interesting requirements, not just 600pp, 700pp and 800pp races, then I'll be happier than I would be if it were 7-10 new cars and 1 or 2 new races.