Platinum is no better for the exit row seat upgrades and the priority waitlisting can mean you do not get the upgrade to business, you are only guaranteed the economy seat. (This has happened to me).
I fly Qantas for work and Cathay for private overseas trips. Qantas have only once given me a special welcome on board the plane since I attained Platinum/Emerald, Cathay were giving me the special treatment once I got to Gold/Sapphire status. (Although they have been more sporadic recently).
The access to the first lounges internationally is beneficial. Don't forget that with Platinum you can use the International Business Lounge whenever you are flying, regardless of One World Carrier or not. You can enter the business lounge domestic at anytime which is useful if meeting friends at the airport and they happen to be delayed.
First lounges internationally are great when flying OW, the Cathay First lounges are very nice, (so are the business ones), the New Qantas business lounge in HKG is very nice although a little cold which they said was due to teething problems with the new air con system. (The New Qantas First lounge in HKG opens end Dec), the old lounge was a toilet. However there is no other benefit when, like me, you are mainly in W.A. Sand gropers only get a standard business lounge at the moment domestic and international terminal.
If you are just shy of Platinum, well worth spending the money on a flight to get it though, but if say 100-120 points or more shy, forget it.