My alt is level 20 now and I've picked up a few contacts my main never got. I think it's quite difficult not to outlevel contacts.
Again, grouping plays a fair part in my experience growth, and there are numerous paper missions.
I'm not even at the stage of chasing contacts by the "fancy" means of badge collection.
There's a players guide on the official forums discussing the optimal way to level from 1-15 which entails picking up loads of contacts on the way. It was a revealing read.
More alts than you can beat with dual wielded Thrash Blades.