If 21 MP against 8MP blows you away, imagine what 60MP would do against 8MP.. feel like selling your car for a medium format digital system? But of course there are more important factors to consider here.
Megapixels should never be the reason you get a camera, crop or no crop. If you feel the need to crop consistently, get a better lens and frame closer. You will be using the sensor on your camera much better.
Since you are shooting sports, you want fast and accurate autofocus, fast fps and general handling which means "up, press button, boom" you got the shot. 5D is not made for this, just like 1Ds is not made for that either. Can you shoot a sporting event with these cameras? Ofcourse you can. You can shoot it with a cellphone camera aswell. But a 1D (as opposed to 5D or 1Ds) will work better for you.
And the only argument against it would be that you will have a hard time blowing up 8MP to a billboard or gallery quality prints in the 1-2m range. So... you have to ask yourself, how many billboards will you be shooting for?
Back in the "days" you could for some odd reason blow up 6MP to pretty much anything and no one complained =) Today its almost like you can't shoot your kids birthday to put on the family website unless it's 50MP.
So my advice to you is stay with your cameras, they will work just fine. If you need to invest in something go for glass. Or possibly a 1D Mk3.