I think there's something about spell animations that makes them not play if the hit is not successful. In my Mist Dragon battle in TfW, once she becomes immune to magic, the spell animations stop showing.
That's pretty much the case. I don't think any monster normally sets their magic evasion to 255 though as most of the time they use the routine like the Mist Dragon (mist form) or the Golbez fight (in the Dwarf Castle) or even the Zeromus battle (Cecil must use Crystal phase).
The more amusing way to look at it is see how monsters use "beneficial" magic on you, like whatever you Reflect off Asura or the EvilMask trying to give everyone Reflect status (or even Rubicant trying to use Life1 on the party when you attack him with Fire magic).
Although, you still get the free healing from the confused Kary monsters as long as you have petrification protection while missing the visual.
