Tommaso, do I miss something or does the Advanced F&R dialog indeed not have a proper "Replace" button? All I see are the "Next" and "Previous" buttons, but those replace the next and previous matches, respectively, not the current one.
As far as place is concerned, I think we can live well without the "Close" button (no dock widget has one), and instead have in the replace section [Replace] [Replace All] [Previous] [Next] (although I have to say that I find the "Replace Previous/Next" idea rather unusual; I cannot remember having seen such an option in any search dialog). Jürgen