Honestly, for in game purposes, there is little need to EV train. As long as you are trained up to appropriate levels that match the Elite Four members, you should ideally be fine. Buy a few healing items, such as Hyper Potions, Revives, and Full Heals, and you should be all set.
However, EV training will make it easier in the long run. If you're willing to spend time EV training, then by all means, go ahead. If you're impatient, just grind and you'll be fine.
