Regarding the first point, Caplan personally estimates that about 80% of education is signalling and that 30% is the lowest figure one can plausibly maintain.
As for the second point, I wouldn't bet my life on it. But I think the case is strong enough that experimental measures in that direction are warranted.
How much value is created through publicly funded education beyond basic literacy and numeracy, which Caplan cedes.
Whether Caplan's proposed changes to the education system are good ones.