Well, I would think that the rate of inflation must be one factor among many. For example, if the token supply were doubling every minute, it would almost certainly become worthless very quickly.

But your point is well taken. All other things being equal, scarcity matters, but in the Steem ecosystem there may be other factors that reduce or eliminate any benefit that could be derived from burning tokens. Case in point, it seems to me that the @burnpost experiment never seemed to have much of an effect on token prices.