Take a look at the picture below, which is a good example of why doors are redundant on one of these cars -
My whole car isn't even as high as the window line on that Corsa, and a door wouldn't have been of any use whatsoever in getting in or out of the car in that space, it was far simpler just to step over the side.
Don't get me wrong, when I went to look at the Sammio demonstrator and talk to Gary J about my order I wanted him to add doors to the package, mainly because I had it in my head that cars should have doors.
Thankfully he talked me out of it by inviting me to climb aboard '66 and asking me if I thought doors would make it any easier to get in and out? I had to agree that they would be pretty useless.
If you already have doors as part of your package I'd consider fitting them as dummies - leave a gap around them but seal them in behind so they don't actually function. Best of both worlds?