I was more thinking of this as a way of valuing international business class. For example I won't take the $9K that QF charge to get to Europe in J, but might value the 256K + $1000 in surcharges against a $5K Finnair fare.
As for Jetstar vs Qantas. It depends. MEL-SYD probably yes. MEL-SIN, no way in business class (JQ business is premium economy), but in economy as both are A330s that leave at the same time, probably would after factoring in food/luggage and purchase of a few movies or TV shows on itunes for the Jetstar fare (which usually means it is more expensive than QF to buy). Mind you moot point, as the surcharges make that sort of redemption ridiculous, worse than Woolie's vouchers.