Aren't the USB ports feeding off of one bus, not many. So the 480 Mbit/s is given where needed, and if one device is using x amount of bandwidth, it will subtract that from the 480 Mbit/s slow everything else down. Maybe I'm stating the obvious, but I don't see a reason for this at all.
Even if you wanted to use it to combine the space and make one super-usb drive...you would still need to have all 4 plugged in. And you would need to set up the RAID on every computer you want to use the drives on, if that would even still work without erasing the data. And God know what would happen if you put them in different ports or in a different order each time you transported something.
This doesn't sound feasible.