You can use the "Show/Hide Logic" feature (a paid account level feature) to hide groups of fields unless the user makes a specific selection "Add another car", or "Upload an image of your car" and then the corresponding fields would be shown.
You would have to include all of the fields in the form and they would be hidden unless the user exposed them, so you would have to choose a maximum number of cars you'd let the user enter. You can copy and paste groups of fields to create the repeating sets.
For some reason all of the tutorials I found related to Skip logic are about "Page logic" so depending on an answer it will skip to a specific page, but the steps to use "Show/Hide" logic to show fields based on another question are basically the same: http://www.youtube.com/watch?v=Xz5jPh9Ul1U
One note, in your response table you will see all of the questions, so depending on how many cars you add when setting up the form the view response table can get long/wide.
Seems like you could have saved yourself some typing and just answered NO!!
Seems like my problem may be better solved with a database-type application. Anyone else have a similar problem where some generic info is captured and then an unknown number yet related items, equipment, vehicles, inventory, building data needs to be captured?
How did you handle it?
I didn't consider my answer a no at all. People set up forms similar to what you described in FormsCentral all the time using show/hide logic as I described but I understand if that solution does not work for you.