I don't train for EV for my in-game team. I also just like to battle trainers along the way. However, if I want to use an underlevel pokemon for my in-game team, I will grind on the grass patches until he levels with my current team. I make it a point to do all the grinding first before continuing on with the journey and use repel afterwards because I hate being interrupted by wild pokemon.
As for post-game, I am very meticulous with the IVs and the EVs although I don't use them much for competitive battling. I just want to see them and treat them as my trophy 'mons.