Ghostery (Safari extension, not program) will add value because it blocks what it calls "bugs," i.e. tracking cookies (Other stuff, too?), from loading, whereas Little Snitch simply alerts you when something tries to phone home, which the blocked cookies don't (reeeally shouldn't, anyhow) do.
I think the two complement each other rather than overlap in functionality.
The new Great Equalizer is the SEND button.