Prices are (imo at least), determined by rarity in the product. There are a lot of people collecting A-League TNP, and most would want a signature from there team, considering the quality of this release.
With a signature being 1 in 78, that translates to 3 boxes, so roughly $300. These box prices are unlikely to change or be discounted, so that value will remain consistent throughout its lifespan.
So if you take the odds at hand, $300 will net you a signature card, but if you're chasing your team, there's only a 1/12 chance of it being yours. Now you can add in the price of selling the other inserts you recieve in the box to that total, but say yu can get $80 back from the 3 boxes on non signature inserts, you've still paid $220 for a random signature.
Now this is where sig value is brought in, I'll use my own valuation of price here, but if someone packs one you could theoretically choose which signature you want, ranging from the less popular teams ($150) or the more popular teams/players ($200). You remove luck out of the equation, take the gamble out of it and most of the time come out ahead of what you would have paid busting boxes.
So player quality doesn't really have anything to do with the value of the card (it will effect it slightly), but just because I can pick up a Mesut Ozil signature card for $70, doesn't mean I'm able to pick up a FBK redemption for $60, because its apples and oranges.
Sorry for the long post
