I like your system, it's nice and simple and converts vancian magic to points magic quickly and easily, if that's what you want to do.
Personally, I'm not the hugest fan of Vancian magic either. It's good for 1 or 2 classes but I like having other options too. Here's two alternate magic systems I've devised.
Alternate Arcane Casting System:
All spells are given a DC; generally the DC would just be equal to 2x the spell's level but some spells I believed to be stronger than others even if they are the same level so in some cases I tweaked the DCs up or down a bit.
Casters begin by choosing a school of magic and learning all spells of that school's level each time they level up (obviously I broke up the 9 levels of spells into 20 levels). When they level up they can choose to begin mastering a new school of spells (and learn that school's level 1 spells, as well as the next level of their previous school(s)'s spells) or they can stick with just the 1 school of magic and get a bonus 'magic die' instead.
Beating the DC requires the use of 'Magic Die' which are D6s. At the beginning of every day a caster's Magic Die pool is replenished. Casters have a number of Magic Die equal to their primary attribute bonus (Int/Wis/Cha) + 1 per level.
Casting a spell requires the Caster to meet or beat the Spell's DC with his Magic Die. The Caster may use as many of his magic die as he wishes, but if he does not meet the DC the spell fizzles. If the Caster rolls 2 or more 1's the spell catastrophically fails and the caster takes D4 damage for every 1 that he rolled. Therefore casting more difficult spells (which require more die) is riskier and carry a greater chance of catastrophic failure. Figuring out how many Magic Die you want to throw at a given spell can be a difficult and interesting decision.
And of course there's room in these mechanics for the DC to be adjusted down by encumbrance or up by the use of magic items. Spells with durations or variable effects can receive bonuses to their effects or duration based on how much the magic die exceed the spell DC.
Alternate Divine Casting System:
This system is meant for a melee-warrior type Cleric or Paladin who uses his spell casting mostly to augment his combat abilities. It wouldn't be suitable for a Priest/Spell-casting-first type of character.
The Cleric/Paladin has access to all Prayers; but there are only a handful: Divine healing, Divine Inspiration (gives bonus to perception/also functions like Weal or Woe), Divine Protection, Divine Wrath, and Holy Smite. There is also a unique Prayer for each deity.
Each of these Prayers has a variable DC depending on the effect the Cleric is going for; Divine Healing for example is broken into Cure Light Wounds, Cure Moderate Wounds, etc, each with escalating DCs.
At level 1 a Cleric chooses 1 Prayer and can choose another at each level up, or he can choose to reduce by 1 the DC of a Prayer he already knows.
A Cleric can attempt all Prayers he knows as many times as he wants. However, each time he does so he must make a Prayer Check which meets or beats the Prayer DC (regardless of the Prayer's DC and his bonuses, a 4 or lower always fails). Clerics get a bonus equal to their Wisdom modifier + 1/2 Cleric level to their prayer checks, and of course some items also grant a bonus. Failing a Prayer Check represents the Cleric losing the favor of his deity. The more times per day a Cleric bothers his deity with requests for divine power, the more likely this is to happen, but a Cleric can never be sure when his deity will get fed up with him. If a Cleric fails his prayer check, he must pray for forgiveness for at least 5 minutes to regain his deity's favor (essentially meaning he can't use any prayers for the remainder of an encounter). Clerics can pray for forgiveness once per day per Cleric level; after that they must have a full night's rest before they can ask their god to grant them power again.
