spy retaining passive invisibility breaks the need to spycheck IMO.
all you need now is a single quote/pyro standing around a sentry nest while the engies go attack, and that essentially locks down a cp/intel, save for an ubered heavy (against pyro) or an ubered soldier (quote).
i personally think that passive invisibility during stabs is fair and consistent, but it does teach players how to use their revolver. against sentries teamed up with other players, however, the nerf sucks hard.
it also makes spies that much worse against even newbie snipers.
remember back when you actually had to know what you were doing to not get stabbed all of the time?