I was looking at this today because the druid in my player's party is an online player, and enjoys having "mana" over spells memorized. I see no issue with that, and happily accommodated him. The issue came up with Spontaneous Rejuvenation where you sacrifice a prepared spell to do fast healing X for 3 rounds. Well, that's not going to work since you don't have actually do that anymore. You memorize spells, and use them in accordance to how many spell points you have.
So I made this rule for him. He can use the rejuvenation ability a number of times equal to the number of spells he can memorize. So for a 1st level druid, he gets 1 base prepared spell and 1 for his modifiers (if his WIS is under 20), costing the proper number of spell points (in this case, 1).
We thought it sounded fair. Otherwise you could have someone doing fast healing 2 on the entire group, and only spending 1 point a round every 3 rounds for a ridiculous number of minutes.