I don't think this would be a good idea because you would be buying a pig in a poke, and it could be very disappointing. For example, it could just be an unremarkable brown dwarf with no other stellar bodies of any kind. For this to be in any way enticing, a player would need to be given some choice.
Of course players can't just be given the choice of "peek" at a random undiscovered system because that would be fraught with all kinds of problems and exploits.
I like the idea that in order to "buy" a system you would need to have fully discovered it yourself first. This way if you discover something spectacular (like a system containing a very unusual amount of unusual stellar bodies, or something extraordinarily rare like a green gas giant), you could "buy" the system and have it named as you wish (or other similar perks).