I cleaned up in my 3.5 men's singles flex league this fall with serve and volley. At the 3.5 level people just aren't used to playing against S/V and freak out as soon as you approach the net. I could have easily won half the points blind folded because they were just hitting the ball into the net as soon as I got up there.
Also you don't need a big serve to S/V at 3.5. Just good placement and variety. I have a relatively slow serve and no one was cramming it down my throat.