I’ve run the numbers, so let’s see how the maths work out.
As I’ve expressed previously, I also have no use for reprinted Power Cards and poor-quality pieces, and I don’t really need more 
.
So that leaves the Spirits. Horizons will have 5 Spirits, and a price of $30.*
$30 ÷ 5 Spirits = $6 / Spirit
Now, to compare that to previous Spirit Island products.
Promo Pack 1 is the only Spirit Island product published thus far that contains only Spirits and their Unique Power Cards. It has 2 Spirits, and costs $15† to buy from GTG’s webstore.
$15 ÷ 2 Spirits = $7.50 / Spirit
So, this suggests that, disregarding all the other content in Horizons, it is actually a better deal than Promo Pack 1, Spirit for Spirit. Each Horizons Spirit costs $1.50 less than each of the the Promo Pack ones, and you’re getting the other stuff too.
So, it turns out that Horizons is actually mathematically worth your money even if you just keep the Spirits (and , I guess). You were right, @TakeWalker!
(The Spirit Island Base Game, Branch & Claw, Promo Pack 2, and Feather & Flame all also cost more $/Spirit, but that is likely because they also include other game components, and I can’t really break up their prices into Spirits and non-Spirits. Jagged Earth however, costs only $7 / Spirit, though, which is still more than Horizons, but actually less than Promo Pack 1, even though it contains plenty of non-Spirit material.)
So, what I will most likely do is wait the two years until the Target exclusivity agreement expires, and then if GTG releases a pack of just the Spirits, I’ll buy that. But if they don’t, I suppose I’ll just have to buy Horizons and just throw out all the reprinted/lower-quality stuff.
*US currency, as of 2022.
†It actually costs $14.95, but I’m rounding because prices that are ¢5 short of a dollar are stupid.