Crossover frequency curves - what should I be looking for?

Generally, you would want the summed responses of all the drivers to be equal across the entire spectrum.  This can change, sometimes dramatically, when listening off-axis where phase-issues between the drivers at those crossover frequencies reveal themselves.  Some manufacturers are better than others addressing those concerns with better driver selection, physical design layout of the speaker, better crossover parts, and more carefully designed crossover, etc.

Here's an extreme example:

https://www.youtube.com/watch?v=TIKOhMyOaPU&ab_channel=GR-Research

Also, speaker price has no necessarily guaranteed correlation on the above.  

That’s a really good question, and the answer is that it’s highly complicated. :) Why don’t you get into speaker building where you can learn all of this and build a nice pair for yourself??

<< he said with an evil twinkle in his eye >>

By themselves crossover points and slopes tell us little, and some may be arguable. For instance, steep slopes may improve off-axis listening but time co-incident speakers (like Vandersteen or Thiel) may deliberately use very shallow slopes.

As a buyer, you should be much more interested in the impedance curve as that's a good indicator of how easy a speaker will be to match with a variety of amplifiers. 

I wrote a little bit about crossovers here. It’s not a direct answer to your question but perhaps it will help get you started:

https://speakermakersjourney.blogspot.com/2016/12/crossover-basics-driver-response.html