I have a 360 and I have both a regular Xbox and PS2. You will be soo happy with the improvement to 360. As said above the PS3 will be about $600 probably (money may or may not be an issue for you) and 360 might drop in price aaround the holidays.
The other thing is that Sony is releasing like 5 million units worldwide and then nothing more till after Christmas. I didn't get my 360 till March, and that was literally the first time I could just got to a store and pick one off the shelf. So basically it might be next spring till you get one.
Lastly, there will be sooo many more games for 360 by the time Ps3 is out. Like you, I play mostly Sports/racing games. NCAA 07 is sick mental nasty, Madden is gonna be the same if not better. NBA 2k7 is supposed to be groundbreaking, as well as NHL 07 with completely re-designed skating physics.