Flat or Satin. Which one to use?

I have a 7 year old stucco house, located in Central Florida, that was painted with flat latex paint. The existing paint is slightly faded, is not chalking and seems to be in good condition. I intend to repaint using acrylic. Local painting contractors and paint stores are recomending the use of satin rather then flat type paint. When I quesion what advantages satin paint offers over flat paint, the response I receive is that dirt will not stick to satin paint like it will to flat paint. I have not had a problem with dirt sticking to the existing flat paint. Is there any other advantage for using satin paint over flat paint? I kinda like the appearance of the flat paint but if there is a REAL advantange like better adhesion, better coverage, better color retension, I would consider using satin. All comments welcome.