There is no such thing as a useless car. Every car can be used in some way, which is what makes this game interesting. I personally enjoy taking a smaller Kei car such as a Mitsubishi Minica Dangan ZZ, tuning it for a certain PP (usually 400), and running it in a 400PP lobby. It might not win, but for me, that's not always what I aim for. As long as I have fun, to me, that's all that matters. I do not care for super cars in this game, since unlike Kei cars and smaller city cars, you can practically find them in ANY racing game involving real cars. Kei cars are essentially unique to the GT series, and I find them a real treat to drive. I have more fun tossing a slightly modified Autozam around the winding corners of Suzuka and getting a laugh out of it, rather than racing a car I know I'll NEVER afford in real life around the same course.
To whoever said Kei cars and underpowered cars in general were useless obviously hasn't unlocked their true potential (or is just a supercar freak running them with all assists on and RS tires). Sure, they might be low on the totem pole in terms of power, but power ISN'T everything you know. Combined with their incredibly light curb weight (usually between 500kg and 850kg), clearly they're suited for tight and twisty courses such as Trial Mountain and Suzuka East.
Whether is be trying to set a new speed record in the Red Bull X2014 Fan Car, or racing Kei cars against bigger and more powerful cars and absolutely shredding them, there's something in Gran Turismo 6 for everyone.
