My 2015 gti started giving me issues around 50k. I was the original owner and always used 93 octane. I also lived in a city (Chicago) so lots of stop and go traffic. Some symptoms I experienced were misfires, harsh ride, low power, power surging when trying to accelerate. One of the flaps on the...
Here's some more info about the clarity. You can also keep your spare without issue. Totally worth it imo and not too expensive. Install is pretty easy and only took about 30-40 minutes.
A lot of people (myself included) just add the Helix sub and call it a day. It's a direct plug and play sub that also has an amp included. The sub removes the lows out of the main speakers, giving them a better "quality" sound. Here's more info.
My MK7 gti se had Fender audio so you may be...
I had a mk6 gti that was bagged. Looked cool when parked but that's about it. Had a couple issues here and there, ended up switching to coils. So much easier to not have to mess with anything and just get in and go.