Fully loaded, the Prime is ~35k, and theoretically has more or at least equivalent features, can travel about 25 miles on EV alone, with smooth switching between EV and ICE modes. However, it feels like they threw all these systems in as feature creep. There's a HUD that's really hard to see or get used to, a lot of your EV info is on top of the middle of the dash in a very cluttered manner, the NAV system / phone system is tough to use - you end up trying to go thru a phone tree to make a simple call, and the phone sync is so bad that the sales guy who tried to demo it with my wife's iphone 8 spent 15 minutes and couldn't get it to work. The same holds true for almost every feature on it - the autopilot was hard to get to engage because there was also the standard cruise control features, and so on.
The Model 3 is amazing for its elegant simplicity. The early iPhone metaphor is remarkably apt here - there are things that could be better, it could be cheaper, and little idiosyncrasies like the door handles are there - but in the end it's a night and day difference, like you're getting Something New, and not just next year's model.
There's a list of hard factual reasons I could go into that played into the decision, but I'll try to cut the gushing fanboi talk short. In the end we dropped the extra 30k on our Model 3 and are ecstatic with it.
I think we'll find there's a lot of early Prius owners, even up to '10 or '13, who have enjoyed their car, bought it partly for green reasons, and when looking for a replacement will choose to bump up to the Model 3.