As far as I can see, the real benefits from trams come with two key things:
1) You develop a network that links up places people want to go between on a regular basis (on that basis, tramline 3 from Waverley, past the University, out to The Royal Infirmary and Newcraighall makes more sense than the current line; as would the Leith/City centre link of the Line 1 extension); and
2) You use the tram as a catalyst to change how people use your city centre (cf, removal of cars from the centre of Bordeaux, Dijon, Strasbourg...)
But "we" fear change...