Ah, I see what you mean now.
I thought you might have been referencing some magic item that gives you the ability to cast rituals. (and, in a way, you were...)
To answer your question, I would have to say it depends on party composition.
If you have a wizard in the party, he can cover all of the truly important rituals.
In this situation, I'd have to say that purchasing rituals, or putting them on your wishlist would not be worth it.
A wizard can learn any ritual. The restriction on them is the skill check required for most of them.
If you have a wizard, he can pick up raise dead, cure disease, remove curse, and you can get them from him for no charge.
He'd have to be stupid not to help you out, especially considering that doing so saves the party some cash.
If you do not have a wizard in the party, I'd say that some of the rituals are worth it.
The teleportation rituals, cure disease, remove curse, raise dead, are all more than worth it because they can save you.
Several others are good contenders as well.