This is a highly personal choice. I'm building my touring bike now and the weight is not something I worry about at all. I've picked components based on their value (quality/price), usability, reliability and comfort. The truth is that unless you're going really high-end the weight of all the parts is close. The difference between a full Deore, Deore XT or even XTR drivetrain is negligible for a bike that's going o be loaded with 30-50lbs pounds of stuff. You won't notice even 5lbs of difference you have saved by buying high-end ultralight components.

From what I see real weight savings come from choosing the right camping gear not the bike itself. Example: I have a cheap tent that we use for car camping, it works fine but it's 10lbs. So I bought a 5lbs REI tent. I dropped 5 pounds by spending around $100. I would never drop 5 lbs by spending even few hundred more on bike components. I also saved few more pounds by paying a bit more for the other gear.