The Figure 3 shows a Machine Vision design. But to achieve the maximum bandwidth on the FX3, the GPIF must be configured in 32-bit. In this case the spi controller seems not available (need to develop a manual spi (with poor performance)
USB3.0 is capable of supplying more power as compared to USB2.0. It depends on the design how much current it needs to draw. USB3.0 controller by itself takes very less power and at the same time can go into very low power states to conserve power when not in use. USB3.0 has two additional low power states (on top of those in USB2.0) that save power even when the design is actively transferring data. So, overall an optimized low power application is possible with the right USB3.0 controller.
That's interesting---what do you mean by 'USB 3.0 takes FAR too much current'? the host is capable of supplying 1.5A but the endpoint can use less, and it should be able to connect in low-speed mode and take as little current as it needs---isn't that the case?