Okay, I buy that scavenger/stash is decent, but I'm willing to bet that there will usually be something better. Harvest is pretty bad, so I wouldn't have a problem with it being last. It can be fine with Scrying Pools, but then again what isn't?
But Cache has no business being in the bottom 5. It has MANY uses, including:
-Decks where you have lots of green/purple/brown, and so the copper isn't so bad.
-Decks where it's important to have junk to trash, e.g. mercenary, forager, etc.
-Watchtower/Trader
-Powerful draw engines that need to build payload quickly (Cache adds $5 to your deck for just $5, and is even non-terminal!)
-Copper cards, like Counting House, Miser, Coppersmith, and especially Apothecary. Okay, these are also weak cards except for apothecary.
-Thin decks that can get rid of the copper quickly, especially with Ambassador.
-Gardens/Duke, but the window where you want a Cache is probably pretty narrow here.
Don't hate on Cache man. I would go so far as to claim that it's better than every card currently in the bottom tier. Really, it's a $5 gold in decks that can deal with a couple coppers, which really is a lot of decks. Copper is not so bad.