Government revenue in two speed economy

Comments on Rob Burgess “Gillard's unhedged liability”, 17/05/2011, http://www.businessspectator.com.au/bs.nsf/Article/federal-budget-Treasury-trade-MRRT-Gillard-pd20110518-GXT3T?OpenDocument&src=sph&src=rot

While I agree with the main argument of the post, I find it amusing that many people including commentators don't apply the same logic of the two speed economy for its reversing effect.

Why isn't the current revenue, with the current extremely high terms of trade, is as high as past expected? Many say it is due to the high $A, that reduced the profits of many firms (the low speed part of the economy), including miners (the high speed part) because a high $A translates the same amoung of profit in $US to a lower profit in $A.

If that is true, wouldn't the $A also fall with it then when the terms of trade falls at some stage?  As a result, wouldn't the effect (a fall) on government revenue also be smaller than what most now fear, due to a lower $A? In another word, the part of now low speed economy will become more competitive and increase in speed.

Of course, there may be a lagging effect that should also be taken into account and it would be useful to estimate how long that may likely be.

PS: It appears that the two speed economy has some in-built hedge in it due to the floating exchange rate.