Does it pay off to return as a previous winner?

Does it pay off to return to Eurovision after you have already won it once? Generally previous winners do well. Some acts have returned over and over again without winning and with variable results. Honorable mentions go to Peter, Sue & Marc from Switzerland, Katja Epstein and Wind from Germany... but let's have a look at the winners: The very first winner Lys Assia returned again in 1957 and