I'm getting 2 new AT tyres fitted so hopefully the do the job and I have a half decent spare. I would still like a second spare so the next project is getting a bigger fuel tank so I dont have to carry so many jerry cans on top. This will lighten the load on the roof hopefully allowing me to take a 2nd spare.
But I might not get this 2nd spare/bigger fuel tank and instead see how it goes with 1 spare and 2-3 cans... that all comes down to money unfortunately.
If you want another decent spare, if it was me I'd buy 4 new tyres and use 1 of yr older tyres as that 2nd spare. As you have only considering replacing 2 at a guessing the other 2 are worn but OK. ? If that's the case I'd go 4 new tyres and then use these tyres as yr spares, this way you know what real condition your spares are in. A spare needs to be just as good and reliable and what your already got on. You may need that spare still to get you another 1,000km before a replacement can be found. In other words it should be of the same quality as the tyres your already using, it's a spare not a replacement tyre.
You have to be weary about buying second tyres, just because they look great, heap of tread etc doesn't mean it hasn't spent it whole life just sitting in the sun. (a killer)
Personally think, if your travelling tyres are a very important if not 1 of the most important. What may seem expensive now could end up costing 5x's as much down the track.
I cannot count the amounts of traveller I have come across "stranded" all because of tyres, such as the spares flat, the spare was so stuffed it only went 20km before blowing, or the spare is such poor /cheap quality it was punctured straight away, even had the wrong size.
Do it once and do it right.