It sounds like your method works well, too. I think the number of layers people use depends on the type of glue and just personal preference. Conti cement is a lot thinner than Vittoria for example. Somewhere there was a study that after a certain number of layers, the rolling resistance of a tire goes up because the tire moves around a little on the bed of glue.
Track tubular gluing seems to have a little bit of black art mixed in, too. I've heard about mechanics using their own home-made concoctions of tubular glue and carpet cement, for example. Before that I've heard stories of mechanics using shellac. And pursuiters apparently used to pull the base tape off their tires and glue a bare tire to the rim, with pieces of cork to fill the spoke holes.
And on the flip side, I think it was either Jan Heine or maybe even Jobst Brandt that said honestly the pressure a tire exerts on the rim is enough to hold it in place in most conditions. Even one layer of glue will "work" for most applications. I still don't trust that, though, but there are stories of triathletes leaving 6" sections of their wheels unglued to speed tire removal during a race.