Voyager 1 now approaching interstellar space

Ive always been a great fan of the Voyager Program.  Launched in the early 1970s, these spacecraft have delivered a significant return on investment and represent (I believe) the furtherest tangible object from man in from Earth, in space.  Voyager 1 is now approaching the Heliopause, the area where the 'wind' from our Sun meets interstellar space.  Voyager 1's instruments recently recorded that the wind particles are now moving laterally not vertically as they approach the termination shock.  I don't understand why we don't continuously send ships like this out into space.  Just think with the level of technology now we could construct a significantly stronger and more robust spacecraft.

http://www.bbc.co.uk/news/science-environment-11988466