Interesting to see this new thread created out of the air!
In terms of costs to earn P1 I suppose it really depends on a number of factors including your flexibility to travel, availability of promotional fares, double status credits and how much of your travel is paid by your employer. Indeed, I reckon there are likely quite a few QF P1 who spent well under $1000 out of pocket to earn P1 since their employer requires them to travel regularly, and puts them either in a Flexible Y fare or in J.
The published requirements for Platinum 1 are that you must earn 3,600 status credits each and every year (no discounts for renewal) of which 2,700 status credits must come from flights with a QF flight number (i.e. JQ need not apply). To give you a sense of how much 2,700 status credits is, a roundtrip to LHR from SYD in J would net you 560 status credits. A return in business from SYD to DFW would net you 400 status credits. In other words you would need to take 5 trips to London in business or about 7 trips to Dallas in business during a given year to earn those 2700 status credits, and even then you would still need to earn a further 900 status credits to earn/keep P1. This easily works out to tens of thousands on QF fares. Is this the cheapest way to earn QF P1? Absolutely not! Earlier this month I flew SYD > AKL (via MEL) and AKL > MEL (via SYD) in QF J for ~$1100 AUD return during a double status credit promotion which netted me 480 status credits. In that respect (and supposing double status credits count towards status credits earned on QF flights), those 2700 status credits could be earned on 6 trips across the ditch so roughly $6,600 AUD. I have no doubts that P1 could be earned for under $10,000 annually provided you book strategically, focusing on sale fares offered during double status credit promotions.
The real question, though, is whether it is worth it and what the opportunity costs are to focusing that much on QF. For the many thousands you spend moving from WP to P1 you could easily have earned mid-tier status on airlines in other alliances (i.e. Star Alliance, SkyTeam) which would provide you with lounges, extra baggage allowance, etc. Case in point, Delta Airlines offers Gold Medallion status for flying just 50,000 miles with them and a number of partners in a given year (and even less if you decide to take them up on a status match offer). Similarly, Virgin Australia offers status for substantially less than QF with their fares often being considerably cheaper than QF (and often with service being considerably better, particularly for domestic sectors). And what else do P1 get you? A signed letter from Uncle Alan? If anything this requirement to fly QF so much is really a disincentive in the sense that you must deal with QF more often with reservations falling through the cracks. I've flown many airlines: Air Canada, United, Delta, American, Lufthansa, ANA, etc., and QF was the first one that lost entire sectors on me requiring me to chase them down to get them to reappear on my ticket!
-RooFlyer88