I am becoming less hopeful about the continuing increase of the exchange rate. The claims that it would track difficulty have not been borne out.
As a professional currency trader, the logic that went into the claim you are referencing simply never jived with reality IMO.
First of all, mining is increasing the money supply. That is an inflationary pressure (devalues the money because the supply increases).
Yes the total number of bitcoins that will ever exist is a fixed quantity, but the number of coins that are actually available to sait demand (remember supply vs demand balance?) is only around half of the planned grand total.
Thus if demand for BTC is not growing faster than the pace of new BTC's being added to the money supply then the BTC exchange rate can only go down, that is inescapable supply/demand basics of all currencies.
The increasing mining difficulty will only ease the rate of inflation of the float, this will only serve to reduce the downward valuation pressures on BTC exchange rates.
The unfortunate thing for BTC holders is that with the float being rather small it is ripe for manipulation by well monied purchasers. This has, for example, been going on in the silver markets for decades. The Hunt brothers are legendary for their manipulation antics.
There is no question of "if" this will happen to BTC's, only a matter of when. History will repeat itself, I just hope all my friends and colleagues get out near the top and don't get burned holding the bag on the way down.