Ritual magic

One of the things I've been thinking about is the "Utility Spells" in D&D. Basically, until a M-U has more than 3 spell slots available, why would he or she memorize Read Magic instead of Sleep or Magic Missile?

The house rule I have been thinking about is allowing certain spells to be cast as rituals. Fantasy literature has no lack of ritual, and it makes sense to me to allow this to happen in D&D. The rules I'm thinking of include:

- Magic-Users may cast any eligible spell in their spellbook that they could memorize, as a ritual, without memorizing the spell.
- Clerics may cast any eligible spell that they could normally memorize, as a ritual, without memorizing the spell. First-level Clerics may cast Protection from Evil as a ritual but no other spells.
- Rituals take 1 turn to cast plus 1 turn per level of the spell being cast. Any interruption in the casting disturbs the spell and it cannot be cast again in the same day.
- Casting a ritual spell requires material components on the following scale. 1st level: 10 GP; 2nd level: 100 GP; 3rd level: 1,000 GP; 4th level: 10,000 GP; 5th level: 100,000 GP; 6th level: 1,000,000 GP. These should be appropriate to the spell being cast and must be purchased in advance.
- Any spell may only be cast as a ritual once per day, and characters may not in any case cast more than 3 ritual spells in one day.

Eligible spells
Magic-User
1st level: Detect Magic, Read Magic, Protection from Evil
2nd level: Locate Object, Detect Evil, Continual Light
3rd level: Dispel Magic, Protection from Evil 10', Protection from Normal Missiles
4th level: Remove Curse, Polymorph Self
5th level: Conjure Elemental, Contact Higher Plane
6th level: Reincarnation, Anti-Magic Shell

Cleric
1st level: Detect Evil, Protection from Evil, Purify Food & Water
2nd level: Bless, Find Traps
3rd level: Remove Curse, Cure Disease, Locate Object
4th level: Neutralize Poison, Protection from Evil 10', Create Water
5th level: Dispel Evil, Raise Dead, Create Food

Thoughts?