Nice shots, Mike. I've tried some simulated DoF in Photoshop Elements before, just using the brush to paint over the areas that I wanted in focus after applying the gaussian blur. The most difficult part of using this technique was making sure that there were no errors, such as the one on the door for the first image.
Back when I only used my compact, I used this effect quite a bit. Here's my attempt from a while back:
What I did wrong in mine and I can also see that you did it in your last, is that I didn't make the other parts of the photo (such as the carpet in mine, or the concrete in yours) around the subject in focus. Thing about it if you were to take a real photograph: your subject would be in focus, and the surrounding subjects or objects would also be in focus. Your last one looks like a miniature model IMO because you didn't keep the concrete around the car in focus, giving it the appearance of a model car with a razor thin DOF, an effect that you can't accomplish with regular sized objects without the use of PP such as your photo, or the use of a tilt shift lens. You can still keep certain areas out of focus to give a sense of depth, like the far background with the building and trees, or the chrome bumper in the foreground.
Also, have you considered doing a bit of HDR? It could look nice on images like these, especially the ones with the reflective cars. The second would be lovely in HDR.