I, personally, think 105 will do just fine for a bike that's only going to see 500 to 1000 miles of touring (not racing, right?) a year. Have you looked at the specs for each to determine what the difference between the two cranks actually is?

I'm confused though. You mention Campy Veloce and Chorus in the same post. Are you building this bike up with Shimano or Campy or a mixture of both?