I agree with the spirit of this comment, but I think you are perhaps undervaluing the usefulness of helping with instrumental goals.
I am a huge fan of GiveWell/Giving What We Can, but one of the problems that many outsiders have with them is that they seem to have already made subjective value judgments on which things are more important. Remember that not everyone is into consequentialist ethics, and some find problems just with the concept of using QALYs.
Such people, when they first decide to start comparing charities, will not look at GiveWell/GWWC. They will look at something atrocious, like Charity Navigator. They will actually prefer Charity Navigator, since CN doesn't introduce subjective value judgments, but just ranks by unimportant yet objective stuff like overhead costs.
Though I've only just browsed their site, I view AidGrade as a potential way to reach those people. The people who want straight numbers. People who maybe aren't utilitarians, but recognize anyway that saving more is better than saving less, and so would use AidGrade to direct their funding to a better charity within whatever category they were going to donate to anyway. These people may not be swayed by traditional optimal philanthropy groups' arguments on mosquito nets over hiv drugs. But by listening to AidGrade, perhaps they will at least redirect their funding from bad charities to better charities within whatever category they choose.
AidGrade is a new charity evaluator that looks to be comparable to GiveWell. Their primary difference is that they *only* focus on how charities compare along particular measured outcomes (such as school attendance, birthrate, chance of opening a business, malaria), without making any effort to compare between types of charities. (This includes interesting results like "Conditional Cash Transfers and Deworming are better at improving attendance rates than scholarships")
GiveWell also does this, but designs their site to direct people towards their top charities. This is better for people with don't have the time to do the (fairly complex) work of comparing charities across domains, but AidGrade aims to be better for people that just want the raw data and the ability to form their own conclusions.
I haven't looked it enough to compare the quality of the two organizations' work, but I'm glad we finally have another organization, to encourage some competition and dialog about different approaches.
This is a fun page to play around with to get a feel for what they do:
http://www.aidgrade.org/compare-programs-by-outcome
And this is a blog post outlining their differences with GiveWell:
http://www.aidgrade.org/uncategorized/some-friendly-concerns-with-givewell