It is worth talking to those who've tried both on their cars, Spoon and Wilwood. I know there's a few out there.
Yes, brakes are somewhat a fine art in development, and it's something we (at FreakyParts) try to do best. We are able to offer kits designed around your specific requirements whether it be a direct bolt on kit, or a larger kit to ensure the extra power you've got can be leashed.
One thing with the Wilwood kit many dont realise is they are available will 4 options with the pistons.
You can either have them with 31.8, 35.1, 38.1 or 44.5mm diameter pistons.
The Spoons come with either 38.3 or 40.5mm diameter pistons (mono/twinblocks)
The standard EK9 caliper has a 57.2mm diameter piston.
Given those specs, the closest match in Spoon calipers would be the twin block (2578mm^2) or the Wilwood calipers with 38.1mm pistons. (2280mm^2)
But... and here's the interesting part. Having supplied both of these calipers (38.1 and 44.5mm), the majority of customers actually prefer the larger pistons. The feedback is more about the pedal feel. For the first 1-200 miles, the reports are of what feels like a spongy pedal, but in reality it's just a slightly longer pedal travel.
After the bedding in has been completed, the majority of customers actually prefer the extra travel as it translates into a better range of application.
If you go for a caliper with similar, or smaller piston area than your original single piston has then you'll have what initally looks like a more responsive pedal becuase it goes from first touch to lock up quicker (the better clamping force from the extra pistons, the better pad coverage etc) but in reality all you've done is reduce the amount of lever you have on the pedal.
On the other hand some people want that, so that's what we supply
If you get the opertunity, give them a run, and see how they feel, as brake upgrades can feel as different as jumping out of your car and getting in a Micra with their massively over assisted brakes. You think they're fantastic, far better than your car, until you start using them in anger and find yourself hitting the ABS all the time.
I do have to agree though, branded Spoon calipers are very expensive for what they are, when you can get something that is at least 90% as good (or even better for some people) for 50% of the price tag