Durability is a huge factor for me. On aluminum rims my wheels would always get out of true after a while, be it road or XC. I switched to carbon years back and haven’t had to true a wheel since.
From a design standpoint, carbon has allowed manufacturers to work on their carbon layups to change the characteristics of the wheels based on the discipline. This is where there can be a lot of variation between manufacturers.
There are a lot of ways to sink money into your bike and the sport, but I’ve never regretted the money I put into carbon wheels.