It has been 14,500 years since a comparable level of technological advance existed on Earth. This technology, which is nothing compared with true knowledge, is nevertheless, sufficiently advanced to become harmful to the human race on Earth in the very near future. Harmful, because it is only material knowledge and not spiritual knowledge."
This line in TP alludes that the Gray Race has accelerated our technology and with their help the secret government of the World no has and has had in their possession superliminal ( faster than light speed ) interstellar craft. There has always been a lot of talk about advanced aircraft projects. Since in the next paragraph goes on about the Bakartinians making the decision to scout the Galaxy to find a new planet to call home this is somewhat of a further validation. So we can infer that the government has had interstellar capabilities since at least since the book was written more than 20 years go.
I'm assuming that the greys you refer to are the grey alien race of abduction fame?
Lets suppose that faster than light speed was handed over on a silver platter to the few that rule this planet. By that i mean only a few thousand individuals 10,000 at best that would have some knowledge on this subject. These people are as stated in TP, conditioning the people of earth to become farm animals and create feed lot system that keeps the 10000 or so individuals in power. This system is very very dangerous as material technology effects our material world, helping keep the farm animals in the pen. A means of keeping animals in the pen is via a system of belief in something called money.
Money provides material satisfaction for the farm animals. Ancient Rome had an economy based in slavery. This slavery economy, made things very cheap for them to do. However... Heron and Ceritebus, invented a hydraulic system and a steam powered turbine engine. The roman economy of slavery failed to recognise the use of such things because the slaves could always do things and carry them around. Hence this new tecnology they gained was lost after the romans leveled the library. By adopting this slavery economy belief they limited themselves and when their civilisation needed to grow, in new areas they couldnt. Rome Failed. As will any civilisation that limits itself on material gain and technology.
Could you imagine allowing modern earthlings out into galaxy to trade material things?