Cellar doesn't map to Storeroom very cleanly since Cellar has +1 action and Storeroom has +1 buy. Storeroom > Secret Chamber makes sense though, since Storeroom can do everything a secret chamber does and it lets you sift first and it gives you +1 buy.
Well, Storeroom doesn't have a reaction. But SC's reactions is really weak anyway.
Not against deck Attacks. Then it's better than Moat.
Which Deck attack? Maybe if Curses are out, I would leave a Curse on top for Swindler. Eh.
Thief, Noble Brigand, Pirate Ship: Should be obvious - don't want your Treasures trashed, leave your Copper for them to play with.
Spy - Leave something harmless on top of your deck, and make sure your one Goons gets in your hand, instead of your discard pile.
Bureaucrat - What's that? No, I don't have any Victory cards in my hand.
Jester - Let's put a Silver there and give you AP for a couple minutes.
Rabble - Thanks for discarding my Ruins!
Minion - Random four cards? I think not. Let's be sure of at least two of those.
Saboteur - Here - hit my Moneylender - I don't need him anymore. Oh, and discard this Estate while you're at it.
Knight - Dame Josephine, you say? I raise you Sir Vander! Awww somebody wost her widdwe Wictory points, didn't she? Gold for me...