I owned a 2011 STI Sedan (same model as '13) for 18months and really enjoyed the car at first. It was fast(ish), looked great, handled well, but then my commute increased significantly from 12mi R/T to 90mi R/T and the glaring weaknesses started to show.
The radio is awful. A.W.F.U.L. Even with an aftermarket head unit, its still difficult to get over the road noise from the tires alone.
The seats are mediocre at best for daily driving. They are "sporty" but offer zero lumbar adjustment or side bolstering. When i sat into my 135's sport seats, it was night and day.
Everything creaks. All dash components, console, pillars ALL squeak/creak in any temperature outside of 70+/- 10*.
The cabin is loud in general. Even with the OEM stock exhaust (not even SPT, thats VERY loud), it droned a bit at highway speeds and there is very little sound deadening.
I was able to basically swap out of the STI into my lightly used 135 and wouldnt go back in a heartbeat. I tuned my STI to what the Subaru community considers stage2 with a set of coilovers, SSK and some other visual modifications and it was a fun car. I took a road trip with it from Boston to Atlantic City and it was a LONG trip with the stiff coilovers even biased to soft.
There is a lot of aftermarket available for the platform now, which is nice. You can make really good power out of the motors IF the ringlands hold up. I never popped one, but plenty of people are more than willing to share their heartache with the EJ25 motors.
Feel free to PM me and ill check back here if you want any more info.