Surely, the Mini Cooper is one of the coolest cars back then, and even today with BMW life. The Mini may be small, but it is no joke. John Cooper did a hell of a job back in the day with the concept of a small car that can still deliver. Another low-HP car that's pretty nice is the lovely Volkswagen Karman-Ghia (correct me if I misspelled), a rear-engined, rear-wheel drive (just like most Porsches, mind you) machine with low HP, but still looks and probably performs lovingly.
Oh, and do you want another reason why to keep "crappy 63hp cars?" The other reason is because you can always add power to make them much faster. Hey, taking a Kei car with Kei horsepower, but giving it as much horsepower as a stock Civic Type R or Civic Si is impressive in terms of power. These cars may be slow, but you can race into corners better than much powerful, much larger cars. Some vintage race cars weren't horsepower beasts. Probably anyone outside of America's Trans-Am series (I'm not knocking this long-running deal) would know of automobiles that may have lacked power, but still delivered on any given Sunday.
Another thing about these sorts of cars is that they shouldn't be looked on as a waste of time. Speaking as an American, America doesn't make low-horsepowered automobiles in the past. In fact, big-bodied muscle cars and high-displacement old beauties dominated most of our automotive past. Also, this is a chance to see different cultures at work. Not everyone in Japan owns a big-bodied car with 400hp and 5000+ cc of displacement. Europe even comissioned smaller cars to try to cure some fuel consumption concerns. You'll see turbo diesels and stuff. To me, that's the only excuse I could make for someone when it comes to racing less-powerful machines. It's probably arguable, but one of the best small cars I ever raced in a game was a tuned Mugen Beat in Gran Turismo 2. I modded it up to 98hp, and it delivered on the track with precise control in corners, great braking, grippy tires, all the stuff you need for a racing machine. Race cars don't have to be Le Mans prototypes and Formula One race cars.
In other words, keep the balance of cars healthy and unaltered. I've actually enjoyed racing things like the Honda S800 Race car to a Mitsubishi Pajero Dakar racer, to even trying out the Honda Odyssey and Toyota Tacoma. I brought myself to love racing these machines, and I don't feel a lick concerened. Just race, already!