Yes for the most part you'd only use a polarizer for sunny conditions.
As for your pictures, I'll try to explain what *I* think is wrong. I'm still fairly new to photography but have been learning a lot these past months. First the idea of using a polarizer in a dark area like your driveway at the time of the day is a bad idea. It would be similar to wearing sun glasses at night, although some people are cool enough to pull it off..lol
The fact that you had polarizer on underexposed your picture.
I'm not sure if a UV/Haze filter would help you. If you have then play around with it and take some with and without, then you decide. I've heard so-so things about them. Some of the hardcore photographers believe UV/Haze filters lessen IQ.
Also your flash is kinda harsh. If you look at the second pic the middle is lit up where the flash was aimed but the sides are pretty darker. You might have been better suited using a tripod and longer shutter speed with no flash.
*edit* your focusing my be a tad off. For car photography you might be better suited focusing manually. I know I've read in camera manuals AF doesn't work well if the subject is very shiney...lol
