What 13ST14XV said...The new Crosstrek is a significant upgrade from the old one as a whole. However, I would not trade in my 14 to get one. It is a little larger, has slightly better power delivery, smoother ride, has a few nicer features, and definitely has a better quality interior. Individually (other than the interior quality), most of these improvements are marginal. As a whole it is a better vehicle. To me there is just not enough there to justify one over the previous generation unless you absolutely need the slight size increase (and if you do, I would suggest a used Outback instead). This of course assumes that your 17 is not in a position that says you might want to consider a new car anyway (for example if it has 150,000 miles on it or is blowing oil everywhere, guessing not if you expect to get 19K trade in). Now if the new generation had significantly more power, it might have been enough to make me want one. As it is, I just do not see the reason to swap from the first gen.
Note this is not me speculating. I have a friend that has the exact features I would get in a 2018+. I have driven/ridden in it several times. It is definitely an upgrade. If you are in a position where you need a new car, I would consider the 18+ over the previous gen if it is in your price range. However, if you do not need a new car, I see no reason to upgrade.
For finances... You do you... I personally do not think there is enough there to justify the additional expense. The fact that you came here to ask about it instead of just doing it leads me to believe maybe you think the same, but that you are also excited by the prospect of a new car. You have to figure that out for yourself.
Except that Eyesight would be a big improvement over a previous gen without it.