Both the drives come with a dock. The USB2 drive's USB2 dock can be replaced by the USB3 dock.
The USB3 version already comes with this. So its a better value than "USB2 + USB3 Dock"
Also where did you read that it needs 2 USB ports.
The USB2 version needs external power and transfers data via USB2 slot.
The USB3 version draws power and transfers data both from USB3 slot.
And about your third point.
The USB3 version is as fast as a regular Desktop Harddrive. If you use a fast harddrive like the WD Velociraptor, it will run as fast as it could run internally (nearly).
It wouldn't even bottleneck a fast SSD.