Yes, there is a visible difference between basecoat/clear and the original single stage. And yes the clear is typically more spectacular, but is not original looking. I have sprayed many cars with both single stage and base coat/clear. I have always used PPG's top of the line with fantastic results. Typical gallon of color is now $500 and the clear is about $200. That does not include the hardeners and such. Like John said, the type of paint you use depends what you are after. The clear gives the color more depth and will never look like single stage.
IMHO, base coat/clear came about because of cost. Just look at the $ difference above. You spray two coats of color and the rest clear. Plus with clear, you can have many specialty finishes and it makes metallic colors easy to fix. So, many good reasons to use a clear top coat besides the look. Since I am a DIY and paint my own cars, there are blemishes. With base coat/clear, I can fix them easily. I am painting the '70 Roadrunner as we speak. See attached. BTW, that is not where the body was painted.