Soffit vents do not "vent" a roof there there so the higher vents can draw outside air up over the underside of the sheathing to keep the air from condensing on the under side of it. Without soffit vents it would be like trying to suck through a straw with your finger over the end of it.
With a tile roof your going to have to have gable vents. They make electric powered gable vent fan with thermostates on them.
Those solor fans do not run fast enough to be much good.
An attic is suppost to be the same temperture as the outside air. If there the same temp. No condinsation can form.
How much insulation is is the attic now? It's far more important to have as much as possible since it were about 50 % of your heat and cooling is lost.
Recommended Levels of Insulation : ENERGY STAR