This update, much like any other updates, is drip feed content which either should have been in at launch or released in a much bigger update catering for all.
New track? Nope. New championships for existing cars? Nope. New AI balancing? Not likely.
The problem with four cars, or three cars, or five cars, is what actual value do they add to the game? Livery editing is one, and for those cartists, great. For many others, it is use of the car that matters most.
If we wind the clock back to GT4 there were multiple special cars of extremely limited use such as the Ford Model T, Nike One and Toyota Triathlon. So including the ambulance in and of itself, is not the problem. The problem is that too much of the car list have the same fate. Outside of custom races or online lobbies - which can fail at any time due to host departure - what can you do with them?
Enter a drivetrain championship? Nope. Try your hand at an endurance race challenge? Nope. Err... Scape? Yes, you can do that.
This is GT7 and the big issue. If you are not an online racer (given the above mentioned lobby cut out, lack of consequence for dirty driving, it's not difficult to comprehend why) then what do you do? Some will point to custom races.
Problem there is a) poor payout, b) poor AI, c) poor balancing and d) pure expectation for the player to do the work for PD
GT4, often regarded as the greatest single player experience (highly debatable) had a custom race feature. However, it didn't need to rely on it. Many players likely never used it, why? GT world championship, endurance races, single manufacturer races, like the wind, Polyphony Digital Cup, Sunday League, MR drivetrain, 1000 Miles, DTM, All Stars... Oh, they're championships!
So, PD, instead of focusing on multiple cars for updates. Why not add multiple championships? And bring back prize cars while you're at it, give an incentive for people to actually DRIVE the cars.