The first point you mention can be discussed, although I am going with chak here that we players decide what has any value and what hasn't. If I start mass producing dragon helmets now and hand them out to every player I meet, their value will sure drop quite a bit, but how would the scent system reflect that fact?
The second thing is that with that small of a timeframe you make it impossible to track down thieves when you didn't find the scents right after the theft happened.