I just wanted to chime in on this thread with both a question and responses...
I have the region 0 pilot and existing season 1 and 2 sets. I will probably get the Gold Box eventually anyway, for the extras; but how does the picture quality look compare to the existing (especially the stunning existing Season One) sets? Can I just sell off what I have, or do I want to hold on to them?
To the person wondering if the show holds up: yes, especially with the quality transfers, the look and feel of the show has a kind of timeless quality. It might not be worth buying the set (although I have gone back a few times) but at least try renting it. Also, there will probably be a lot of fanboys (liek me) selling their existing copies of the separate pilot/S1/S2, as they pick up the Gold Box for the new extras... if you can settle for those used, they'll be cheap, I bet!
To the person wondering about the movie: Let me repeat what others have said, do NOT watch the movie before watching the show. Not only will it spoil the show, but a lot of references will be lost for you.