I think you're right on that! (Trading up to 1.0 / 1.5 10G)
That said, I'm currently looking at options for intake and exhaust as you mention. As the Injen is ~£300, I've gone for the creative route first of a build-my-own system, using a RAMAIR Cone filter, MAF Adapter and 75deg 3" pipe from Spectre performance in the US. (As well as a cheap PCV filter to pop on the pipe)
All in cost for the build my own intake is ~£120, most of which being the costs of the US Parts; I could've probably done this cheaper if I'd just ordered their MAF adapter and sourced the other parts locally, but it was just easier to get it as one.
I'll update once I've got it put together - Hopefully it fits!!
Once that's done, next on the cards is an exhaust change. As you mention, there's 2 back boxes on the 1.4 - One on the centersection under the driver, and a second at the rear.
I'm thinking of having a new B-pipe / centersection fabricated with a "cherry bomb" style resonator - Not so much for performance, but to make the sound slightly less sad-lawnmower