I have noticed that the higher level you get the better the Pokemon that appear around you seem to be. But in the beginning its worth it to catch everything you can. Since you get XP and stardust. You also get XP when you evolve Pokemon which is nice when you are just a few xp away from leveling up.

I snagged a Krabby today while swinging by a friends work. Then went to Costco and was bummed that the entire area was empty. I need to hit the PokeStops hard right now, I only have like 10 Pokeballs right now. ^^;