Okay... I'm quite sure that One Piece is Roger's treasure... the treasure that he got from plundering and pillaging or bounty-hunting and the like.
Yes, Shanks and Buggy were both on Roger's crew.
I think that what you said about Shanks and Buggy not being around... should be restated as "I don't think they were around when Roger hid One Piece." Why? Because... they were in his crew... and it wasn't just them, there had to have been lots of others. If they weren't around to get One Piece, then the rest of their crewmates would have been. The only problem would be strength... because there is a possibility that Roger hid the One Piece in a place where people only as strong as him (or the YonKou at this point) could reach... or maybe only people who could read the poneglyphs (Robin and the Oharans) had the ability to find it.
Iono... but I'm quite sure that A) One Piece isn't technology hellbent on destroying the government, B) Dragon =/= Roger, and C) the ancient civilization spoken of in the first post was wiped out in the hundred years of Lost History and only a few things (the poneglyphs and god weapons Poseidon and whatever) are the remnants of said civilization.