Lets talk 2017-18 swaps on to 2013-16 cars
 

Can the gauge cluster be swapped into earlier cars?

Can the steering wheel with head unit control be swapped into earlier cars?

How about the head unit? Would the steering wheel have to be swapped together with the head?

What would the full 5hp red intake manifold swap kit look like?

1. Sure, if you know how to re-wire and reprogram the gauge cluster.
2. I don't see why not, again same answer as number 1.
3. Again same head unit as 2016, you can just need to rewire. Steering wheel doesn't have to but since you're trying to swap em both, go for it.
With those questions answered, it's probably easier to buy a newer gen brz.
4. The red intake mainfold would look exactly the same the new one. Same engine just red manifold. There's pictures on google for reference.

By the time you were done you would have paid as much as you would lose trading the car for a new one. It is not a straight nor easy swap as many things would needed to be added for everything to work.

The manifold is just one part of several that all add up to give the 5 hp. It does not give the increase all on it's own. You would need to be able to tune to take advantage of it and the other changes.

The head unit is pretty crappy imo. I don't really see that as an "upgrade" unless the earlier ones are somehow even worse.

I'm also not a fan of aluminum as the material for the intake. It's cool they changed the runners a little bit but I prefer the thermal characteristics of a composite.

Why bother 17 not really much better, other than styling, if you like the new over the old.

The styling being better on the 17 could be argued too.

For me I'd just like the radio controls on the steering wheel and maybe the display on the gauge cluster. If the steering wheel was plug and play I'd probably find one and change it out.

Totally agree. I prefer my 16 over the 17. I like the stock 17 wheels more than the 16 stockers, but not worth changing. If spending money it will be on aftermarket wheels.
Maybe the spoiler is nicer.

I agree that it doesn't make sense to swap everything from a '17 car. Maybe some specific parts might worth the effort like the intake and exhaust manifold. I am aware of one user who swapped the intake manifold. @Trap63: Can you share some experience from this swap?

This.