You have to bare with those commentaries, I find. They are indeed VERY boring, you have to be in the mood. I haven't read Fraylings Book yet, and funnily enough, I have loaned it out twice from my university library, but I never have the time. :-
The commentaries are really boring, but there are some right jems in there. Because Frayling knew Leone, and had talks with him, you can't get that sort of information anywhere. I also love all the producers and guys that were involved with Leone talk about him, Alberto Grimaldi I think is another one. The stuff they say, as boring as they sound, and as difficult it is for them to finally finish a sentence, they give the kind of information Leone fans want. Leone stuff is quite rare.
Milius I think had something to do with the Duck, You Sucker stuff as well as John Ford's The Searchers DVD.
Also, I love Scorsese's commentary on his films or on other films (regardless of whether it's an actual commentary track). Scorsese footage is also quite rare to find (not as rare as Kubrick though) so anything with Scorsese in talking - I have to have. I heart him. :-*