Why Did We Come Here Again?

Although i'm not much of a fan, the new Star Wars film is breaking all sorts of records and it has led to many discussions around my favourite subject, Space.
While the idea of humans travelling between Solar Systems does appeal, the nearest Solar System is 4 light years away, or 24 trillion miles, and as the top speed of our rockets is 20,000 mph, that's a 137 thousand year trip and it wouldn't be you setting foot on strange new lands like Captain Kirk, it would be your future generation born in transit.
The good news is that if there was a marauding hoard of Alpha Centurions plotting to explode that third rocky planet in the neighbouring solar system, it would take them the same amount of time to get here and by the time they arrived, the later generation of ET would have forgotten why there ancestors set off and probably trade beads with us.  
That's why i'm not worried about an Alien Invasion anytime soon, on the Apollo 10 mission, NASA pushed the capsule to 24,790mph and decided that was as fast as our mostly-water bodies could handle without causing permanent damage to the astronauts so if that is as fast as we can go, that is as fast as they can go also.
Unless that is they are not carbon based life forms at all and their bodies can sustain higher G-Forces than us humans, if they can reach light speed they would be knocking on our door within 4 years.  
Being a more advanced civilisation, they may also be able to exploit loopholes in known physics or through paradigm-shattering discoveries and all they would need on the trip is a packed lunch.
Maybe it wouldn't be such a bad idea to invent blaster cannons then, just in case.