Right now, probably the best place to level up would be Victory Road. It'll take some time, but if it gets you past the E4 easier, it's worth it. Here's what I do: Get a Pokemon that knows Thief, and take it up to route 210. There are wild Chansey in that area and you can try to swipe a Lucky Egg off of one. I got one on my third try, your results may vary.
It'll make levelling up go a bit faster, especially if some of your Pokemon are traded ones.
edit: oh yeah, once I can finally reach Pal Park, I'll have plenty of junk to trade. Jirachi, anyone?