Trade-in or sell? Never. (This forward looking statement may turn out to be false at some point. You were warned)
Upgrade, hell yeah. No model 3 should suffer through being stock if you want something different. Tint it - I tinted it myself for $50 and it's not perfect, but it's good enough and gets the job done.! Upgrade something! Make it yours! My power frunk and power trunk are a delight to use and people love seeing it (less so now that new M3's have power trunks). I just received the LED replacements for the rear reflectors and can't wait to see them installed. My car may be a 2018 but it has USB-C charging ports, and I'm considering putting the new acoustic glass in.
I'm at 93K miles. When I hit 100K and lose the powertrain warranty I'm seriously looking at upgrading (3rd party) and adding a front motor. The LR-RWD seems like it can beat almost any car until 30-40mph, then it starts to get limited. And RWD cars really have trouble pre-heating for supercharging since they can only extract additional heat from the motor when it's not moving, or at slow speeds. AWD cars use the front motor for heating up the battery while driving on the freeway. I can easily see a "preheating for supercharging" message for 100+ miles on my LR-RWD.
Also, I have a theory, which may not play out, that cars purchased with FSD prior to sometime in 2019 will be given free hardware updates until the car gets to L5. Cars after that "may" have to pay for those upgrade. Just a theory, but it would make sense given the financials, and the changes in FSD description from "L5 let the car do it by itself" to "FSD includes Smart Summon, NOA, and city streets"