If you're getting good download then the booster won't help with upload speed, which is limited to 3Mbps regardless of plan on Gen5.
The wifi extender/booster extends your signal (EDIT: meaning it extends the reach of the wifi signal when you have areas in your house where the wifi is fair or poor), but doesn't increase speed (and like Mark said, upload speeds are 3Mbps max). HughesNet doesn't work well with VPNs, unfortunately.
Do you notice any difference if you connect directly to the modem via LAN cable?