I always just thought that Persona 3 had cooler animations than Persona 4 did, both because of the evoker animation and the different critical hit animation depending on what weapon you had. 
Still, I never really found them anything but a cool animation. I also liked how all of the dudes killed themselves in different ways. Minato put his gun at his temple, Yukari put hers under her chin, etc.,etc.

The use of evokers was appropriate for the tone and story of Persona 3.  To be honest, the only thing that bothered me was the way that the characters' weapons would magically vanish when they used them.  I mean really, where do Akihiko's boxing gloves go? :P

I thought it was interesting, but got stale after a while, like the animations took too long...Also the stupid quotes that the party members said when you got all the enemies down "I've been waiting for this!" OK WE GET IT, YOU WERE WAITING FOR IT NOW SHUT UP!

If they weren't there and all the characters used cards instead (or even something else), it would really affect nothing. They are there to look cool, and as an animation to justify why the Personas appear. I hope they are never used again.