I think there should be a way to fail casting the spell, like heavy armor spell failure and such. I also think you should be able to miss, but it should be dependent on the individual spells. If you've got a spell that shoots out an energy bolt like a gun or an arrow, then it should be dodged like a gun or an arrow (but potentially pierce armor or something, it depends on the spell).
Some spells, though, would be much more difficult to avoid. If you turn a football field patch of ground into lava, it is going to be very difficult for that to miss.
My point is, whether you use reflex saves, fortitude saves, will saves, dodge bonus, armor class, or whatever to dodge a spell it should be different for each spell. You could also have some sort of anti magic field or armor that works against all spells if you wanted, but against a normal, non magical person or creature it should be spell dependent.