To use tangible rewards, or not to use tangible rewards?

While I am against the consistent use of tangible rewards--pencils, stickers, stamps, bookmarks, etc.--as a behavior management system in a full-time teaching situation (see research on motivation by Harter (1981), Lepper, Greene and Nisbett (1973), Cordova and Lepper (1995), and Whyte (1979), as well as others) because I feel it sends the wrong message about learning and decreases student motivation in the long run and eventually becomes ineffective as a behavior management strategy, I can't argue the practicality of using tangible rewards as a substitute.  In a full-time teaching situation (during student teaching) I would occasionally and sporadically reward students with tangible rewards for showing improvement, which I didn't feel harmed the students' intrinsic motivation.  Following this logic, utilizing tangible motivators as a substitute should not affect student motivation in the long run, and should not become less effective because of the short term in which they would be utilized, but still I don't feel right about it.  I know substitute teaching is sort of an artificial situation, but I still feel like I'm going against my beliefs as an educator.  It has been effective along with my other behavior management techniques, though.