There are maybe 2 business class seats (J#) and, I don't know .. 1? First class (F#) seat allocated for points redemption on Qantas international flights, I believe. Others may correct me on the numbers, but its not many, considering the demand! Anyone can request extra seats to be released to them, but only those with status (Plat, Plat1 and Chairman's lounge) have a reasonable chance of that being allowed by Qantas.
Yes, Business and First redemptions are a good way to spend points, mainly because with all Award seats, Qantas charges high cash 'fuel fines' and other charges so if you are happy to fly economy, its often almost as much to buy a sale economy seat than redeeming points and paying the cash charges. You still pay these with J and F redemptions, but you get more bang for your buck!
Programs are always changing, but some airlines, such as American and United have much lower cash charges with their points ('miles') seats.
Australia and the world is awash in FF points. People who never fly in a 'revenue' seat can accumulate millions of QFF points and they are after the same few seats per flight as you may be (and me!)
I have been a long time Qantas flyer, and still am, but I fly much less with them now (maintain Platinum via client paid J flights to Nth America), and I have steered my credit cards towards Velocity points earning (where I am a lowly Silver) and I push them through to Singapore Krisflyer. From there, I get access to the Star Alliance network, which I also have via my membership of Air Canada Aeroplan (that's NOT such a good program!). So I cover many bases.
If you look as though you might be earning a lot of points, why not get a card that earns direct or indirect on Qantas, and one that earns on Virgin - the latter either to fly Virgin, or one of its many partners.
You are way ahead of most by coming here - there are ways to improve your chances (I don't know half the tips!). Trawl a few threads to get into the lingo and ID the issues, then keep asking away
# Award seats in business aren't given the 'J' symbol nor first 'F' but some other letters, which I can never remember.