Good questions CD, as to travel and assuming "they" are out there hypothetically, and great distances away, they would firstly require a huge power source of some sort or..... be able to bend it like Becham.... 

So perhaps another track would be, hypothetically of course, to be able to use "Time Slip" to their advantage? Could possibly be the answer to our limited travel into deep space?

We can actually observe this warping of space-time, produced by the mass of the Sun, and see the slight bending of light or radio waves, passing close to the Sun.

There have been several convincing occurrences mentioned.

http://www.charleslindbergh.com/history/timeline.asp

http://www.labyrinthina.com/electronicfog.htm