Save now, and upgrading a subclass later will be easier.
These new Upgrade Points are used to pick out precisely the things you want to unlock. You don’t have to use the right away.
Once you hit level cap it becomes harder (more time consuming) to gather UPs so if you’re wanting to unlock everything in any given subclass you’ll be in for a long grind.
That’s why I’ll be saving some of my UPs until I can dump them into the subclass of my choice.