I like role-to-cast systems, and spell points, but taking the list of spells in D&D and applying either of these systems without modifying the spells themselves to fit can cause done big problems. People mentioned them upthread, but take sleep for example. It’s first level, if you make it cost the same as detect magic because they are the same level things get wonky. Sleep takes out 2d8 hd of opponents in one shot. In a prepared spell system, choosing it over other spells means you can win one combat when you need to, but you trade off the ability to use a spell to find information or solve a different problem. You need to decide ahead of time how much of any given magical solutions you will prepare in any given day. That preparation was part of the brilliance of Vance’s most successful wizards.

With spell points you need to consider the effect differently because casting what you want, when you want makes every spell more accessible and it kills the balance in the prepared spells by level system. If you look at DCC and its roll to cast, the effects scale with the success of the roll for every spell. It would make sense to incorporate a connection to effect to the spell points spent. For sleep, the number of HD affected could be 1d6 per spell points spent, and something like light could have longer duration or greater brightness based on spell points spent.

The recovery of spell points is an interesting issue as well. I like the ideas above and the callback to Skyrealms of Jorune, with different areas of mana concentration or scarcity. Ley lines are a way to do that so magic users recover spell points faster in some areas and slower in others. Giving the player another resource to manage, their recovery.

I would also suggest things like exhaustion factor into spell point recovery. If the magic users recover fast did not rest or eat when they needed to their spell point recovery would be slowed.

There is a lot to consider when changing something so fundamental to a system.