Depends.
Do you have any other Apple devices that keep you wanting to stay in the Apple ecosystem? Such as an Apple Watch, Mac, AirTags, Apple Card, etc?
Do most of your contacts that you message have iPhones and use iMessage?
Do you use FaceTime?
But I think overall the Pixel 6 is a better device than the iPhone 11. As far as if I’d trade it in for $350 it depends on how much I paid for it and how long I’ve had it. If I had it for at least a year I’d say that’s a reasonable trade in since it’s about half the cost.