Well I am looking at the mentalism ritual, it is basically as the essence one changing 2 points mainly: it has more risk (looking at the maneuver table compared to 'power manipulation' one used for other realms), but it compensates with less categories (only 5), I see it good if used with other ones.
The main problem is that it has the same use, with 1 skill you have access to many spell effects, and that is my question, if it is appropriate to use ritual in that way.
For example, in mentalism, see that with 2, self and other intelligent mind any mentalism user have access to all healing spells.
Then, this can destroy the concept of choosing a profession to have access to certain spells, pay many DPs to have many spell effects (see that for a spell user the cost is the same, 4 DP, 1 rank in a spell list and magical ritual). And as we know for combat spells rituals are useless, but for non-combat spells rituals can substitute spell lists in a cheaper and very flexible way.
The main problem is surely that your players have not tried enough the rituals, but I am using it with my magician and for that I ask about it, with a single ritual, enchant variable, I have access to all spells like runes, symbols, inscriptions and all those type like, al them are non-combat spells and it is not important is you delay casting them, then, where is the reason to be a runemage profession and spending so many DPs to adquire all those spell lists?.
Is for that I think rituals should be used in another way, or limit it in any manner, it is very easy to abuse for non-combat spells. Maybe the original description?, it says about "enhance spell effect outside normal parameters", that could be increase the range in an unusual way, for example to cast a curse to a target with some part of him (like in the voodoo) so you enhance the range in an unusual way, etc.
And, as I mentioned before, for some effects typical of rituals, like invoke a god or create special alchemy effects.