just checked some prizes out of curiosity for that route and found tickets starting from 400 EUR for 2 adults and two kids (unless you have to travel on the most expensive dates). Make it 600 EUR but it still does not sound like a big difference and you are not factoring in the depreciation and maintenance a car costs for a long trip like that. Financially i don't think it makes a big difference, it's probably about convenience in the end.