Lol, good questions, never heard of the hydra though and I don't know the difference between the gold and silver, but I always thought it was really a different era - as it grew in popularity I guessed he changed the casing, but people seem to ahve a preference. I suspect the priciness will change with the new Klon. You can get a good clone of the original from builders listed in TGP for a reasonable price.
Good morning! I can't believe that you've been on TGP for 5 years and haven't been Klon cloned to death! Basically a true clone is going to need a double ganged volume pot and a charge pump. If it's got those, it's probably accurate and will sound somewhere in the ballpark of how it's supposed to sound. OTOH, you could build one yourself (there's instructions on components and circuits at Freestompboxes.org).
The silver and gold Klons were built using the same PCB, same components and by the same guy. He says there's not difference in sound and his ears are as good or better than mine. I can't hear a difference between the two.
If it were me and I could live a few more months, I'd wait for the new KRT to come out (Klon reissue by Bill Finnegan). It'll sound great and it'll retain its value better than a clone.