I live on the edge of the world, and bought this car because of its low fuel consumption.
I travel on dirt roads often, and I think that this is where the rattle started on the rear window.
Generally I really liked the car. The car however was not for me. The car does have low fuel consumption, yes, but the car does not have any "kick". So if you are buying the car to drive 90% of the time in a city - then yes, this car is for you. However - if you plan on traveling more than 7 hours at a time at times in this car, then it is not for you.
I have found that even though the Spark does 120km/h, it does not really have the power to overtake other vehicles quickly. It especially does not like wind. So overtaking a semi for example is really not a good idea, and don't even get me started on windy mountain passes!
I loved my Spark, really though it is designed for city living and definitely not anything else. I got 15km/l traveling at 120km/h, the fuel consumption is fantastic, but the compromise on space however, for me was not worth it.