It is a stage 1, so Rare Candy is not required, and it is easy to get into play-- for example, if you are able to use Call Energy on your first turn and a Bebe's Search on your second, you will have a turn 2 Claydol
Turntimber Symbiosis comes into play untapped when needed, further lowering its opportunity cost, and since green decks tend to have big finishers like Craterhoof Behemoth, being able to dig seven cards deep in your deck to find them is quite powerful
There isnt really room for tweaks on this design, so theres nothing for WotC to do but commission new artwork for Negate and send it back out for an encore every year or so
Gemstone Caverns: A close second is Gemstone Caverns
In an EX-heavy meta, this is invaluable