I will have accumulated about 75,000 Krisflyer points and 140,000 QFF points by the end of the year.
About 35,000 Krisflyer points will expire shortly.
I am looking at the best use of these points.
Perhaps a trip to Singapore or Hong Kong, flying SQ one way and QF the other, booking economy and upgrading with points.
Is this a good use of the points?
I intend travelling with Mrs Graemeha, by the way.
Bad use of point. Whatever you do, unless your company is paying for your trip or you need the elite miles to qualify for gold status, do not waste KF point on upgrades. Reason:
1. You need to buy most expensive flexi fare to be eligible for upgrade.
2. Points needed for upgrade is about as much as a redemption ticket. From memory, AUS-SIN is 45000 upgrade, 46850 redeem outright. You get the same inventory anyway, ie. if seat is avaiable for upgrade, it is available for award redemption.
With your situation, unfortunately I have to be honest with you, there is not much you can do with 75000 miles for 2 people, either upgrade or redeem an award ticket, you just haven't got enough. You can redeem economy one way x 2, but you still need to pay for fuel surcharge which is about $200, and you still need to find a way to come back, you might as well buy discount economy fare, which sometimes can be as low as ~$600 rt.
The question is, do you have any credit cards points that can convert to KF or VA points? If you do, you can top up your KF account to enough points for redemption of 2 x business class to SIN (With VA, just convert to KF). If not, you can consider:
1. Sign up a CC with huge sign up bonus that can be converted to KF points. Citi signature card and Westpac black altitude all offer good sign up bonus.
2. Buy Star points from SPG. They are running a promotion at the moment which gives you 25% discount and you can convert to KF points. But you need to have a SPG account that is at least 14 days old, which I am afraid that you can't make he promotion deadline which is 31 May.
Worst comes worst, you can always convert your KF points to VA points to prevent it from expiring.
(You can always let her travel business while you travel economy.

)
With your QFF points, you do have enough for 2 x J SIN-AUS. But availability on QF can be hard to find. Emirates might be easier though
Addition:
One thing I forgot. You can also purchase extra miles from Singapore Air as long as you have 50% of the miles needed for redemption. In your case, to have 2xJ AUS-SIN, you need about 93700 miles, since you have 75000, you only need an additional 19000-20000 miles, which you can purchase t USD$40/1000 miles from SQ, a total of USD$760-800, roughly about $1000. It's not cheap, but it is certainly cheaper than buying 2 flexi economy and get an upgrade (which you don;t have enough miles anyway, so you still need to buy).