I mean, you shouldn't blindly spend money on anything, it is always better to do research and make your own assessment of a products value.
That being said, I think the odds of CK3 feeling like recent Paradox games at launch is significantly lower, for the simple fact that they are still using the mechanics of CK2 as a general base. If you like CK2 the odds are pretty high that this game will feel similar, for the simple fact that they aren't really starting from scratch. There are features CK2 has that this one wont at launch, but this game also seems to have features that CK2 doesn't as well.