The Question is simple. Let's say you want to buy a Mercedes-Benz SL in Real Life, you can choose between SL350 all the way to the SL65, right? So, Sholud driving game follow that path as well?
As far as i know, there's 4 examples of game developers' take on engines. First, they offer it in dealership as different model like Gran Turismo. Second, they didn't offer it at all like Grid or any other NFS Series. Third, they offfer choice of engines like Euro Truck Simulator 2. Fourth, they offer the engine choice as an Engine swap like Forza and NFS Shift 2.
The Upside is, if they follow the example of Euro Truck Simulator 2, you can feel the difference between cars that have different engines. I mean, if you bought a Jalopnik Edition Brown BMW 120d it won't feel the same as the pedestrian 120i. It will have different handling, different fuel consumption, different weight, etc.
But the downside is, i think it's going to take a very long time to model each cars with different engine and different noise and different character, so maybe the game will take longer to develop. What do you say guys?