So is there any semantic difference between using vár with an accusative object and with a sublative object?
In German you also say "Ich warte auf das Auto" literally "I wait onto the car".
Standard English is 'wait for', not 'wait on'. But you do hear 'wait on' in some dialects in casual speech.
I assume in Hungarian if you were to 'wait on' the car, you are already sitting on the roof of the car and waiting for something else. This sentence implies that it's the car you're waiting for.
Meaning that you're sitting on it? It seems to be incorrect because "-ra" would imply movement (although here it works specifically with "vár").