I like to perfect those Pokemon that I care for. It's an accomplishment for myself and to them. I must have stated this 10 times already, but you can breed with a Ditto holding an Everstone. And the baby will have the nature that Ditto had. So getting nature isn't hard. The hard part may be to get those Dittos, but they can be found really early in the game. I believe you can get them near the patch of grass just before Goldenrod. I don't have my game, so I can't 100% confirm that, but I'm pretty sure that's right.
As for EV training, I find them not too bad. I generally beat the game first and then go for nature and EV. EV training may seem tiresome but it's not too bad. The hardest part is keeping track of how many EV each Pokemon have. I usually give Exp. Share to 5 other Pokemon and give the first Pokemon an EV-enhancing item that lowers their speed, but adds a +4 EV to the respective stat. That way, I can train the first one quickly and slowly add up the other 4 in my party. Once the first one is finish training for that stat, I switch them out and since the other 4 already started, it doesn't take long to max them out.
This only works with Pokemon that have similar EVs. Most use Timid with 252 Sp. Attack / 252 Speed. Most Pokemon will have Speed EV. But you can figure that out. Just put Pokemon that want to EV train common stats in your party. And if you don't want a Pokemon with a certain stat, take off the Exp. Share.