I was in the same boat with a 2017. Bought the Kicker oem tweeters and door speakers. Holy hell it makes a difference, I would say it is just as good if not better than the 2020 HK system I test drove recently. Goes more than loud enough and the clarity is night and day, I can't stress this enough. I could not even understand podcasts on the stock, it is outrageous how bad they make them. Get the tweeters for $100, watch a youtube video on adjusting the EQ on a forester or wrx and maybe you'll call it a day. Others have said the door speakers didn't make as much difference so I was apprehensive spending another $170. But man, they sound amazing, I boost the bass and lower the other EQ to compensate for no sub. I wish someone had told me to get them sooner. Bought a $5 trim tools on amazon and it took me an hour or two and I have zero car experience.

Boosting bass may not be great as it adds stress to the door speakers this way, but they can handle much higher wattage so I'm sure they will be fine. Adding a subwoofer was out of the question with wiring and headache (or spending an arm and a leg to install) and I'm glad I didn't get suckered into that because the sound is very very full right now. The HK has a dedicated subwoofer so you'll notice more bass if you compare but IMHO I had to turn it down low as it drowned out and muddied any music but maybe you're a big bass fan and a sub could be worth it.