Fully agree on the importance of initiating more robust evaluations in the NGO sector. This is where a ton of programming happens, so there is a huge potential for learning. And some INGOs are already leading the way (e.g. IRC).
Unfortunately, the real challenge is not a lack of understanding of the IE methods (the intuition behind these can be understood pretty quickly by non-economists as well) but, in my experience, is more often related to a range of other factors, including: failure to plan the evaluation during program design (i.e. difficulty of connecting researcher and implementer early enough), discrepancies between what the researchers wants to evaluate and the organizational learning priorities, fear of the results by the NGO leadership, lack of IE skills locally (flying in people from abroad is not always realistic in part because a lot of handholding is needed for organizations new to IE), lack of power for the smaller NGOs and programs, etc.
It would be interesting to get the collective wisdom of the Development Impact team to mitigate these and other common challenges. For instance, I think promoting more mechanism experiments is promising, as these are more operationally interesting for implementers than "works/doesn't". I think we also need to provide more opportunities to young researchers (during PhD or shortly after) to take on smaller IEs which can still be useful for learning - those evaluations the established researchers don't want to do because they wont make it to the top journals, etc.
Finally, here is another resource on M&E and IE that we developed at the WB with an NGO audience in mind, focusing on employment programs but applicable to anyone:
(available in English, French, and Arabic)