One thing to keep in mind if you are using premium tires. I bought a set of Schwalbe Marathon tires. They lasted me for about five years. In all that time, with no flats I never had to change the tubes. That is, until one day I had a catastropic blow out from the valve stem separating from the tube. Luckily I was on a dirt path when it happened and all I got was a face full of dust and a sore stomach from landing on the handlebars.
That stem will wear out from normal airing of the tire. From now on I'm changing tubes every year.