I've found I appreciate particular sets of qualities. Novel solutions to engineering problems, and mechanical simplicity are two of the big ones. I love the simplicity of a vehicle like the Model T, with its transverse springs, two speed planetary transmission, and unusual but perfectly logical control layout.
It's the honesty of the machine, nothing is hidden, and everything is functional, which I find so interesting. It was, of course, plenty innovative in its own time, being the first affordable car with a four cylinder engine, as well as having other interesting features like a torque tube which sealed in the drive shaft, away from dirt, and did away with the need for a panhard rod to locate the rear axle - or the parking brake which is interconnected with the clutch so a first time car owner would never forget to release the brake before driving off.
Then there are cars which aren't just simple, but brilliantly simple. Like the Citroën 2cv with its clever interconnected suspension, roll back roof, and neat tricks like removable seats, and headlights which can be leveled from the driver's seat. Or the little Lloyd LP400 which brought front wheel drive to the masses and inspired cars like the Trabant and the Suzulight 360 (which in turn inspired almost every Japanese front wheel drive car which followed).
There are also cars which may not be particularly clever in and of themselves, but which are the result of crafty thinking on the part of their manufacturer. Such as Studebaker's Lark which, due to a lack of funds, was essentially a full size Studebaker with all of its overhang cut off and re-skinned in a new style which would set the trend for compacts yet to come.
There are also cars which may not be very simple, but which are still innovative or novel, and though I admire a few of these for their daring, I still appreciate the simple ones more. So what is it that you appreciate when looking at vintage vehicles? Share your thoughts please.