is the steel and carbon fiber worth the extra $50?
Yup, but not because it is stronger. I don't have the G-10 model. I have other G-10 models but non of the linerless ones (only Manix, Lil'T, etc), but quite frankly, I find even the FRN models plenty strong. The reason, why the CF Mili is worth every penny IMHO, is because it is simple an extremely well made knife. End of story. Lockup is rock solid and the knife has a good substantial feel to it. I did grab the blade with protection and torqued the handle to see whether I could make it fold up (it is my first liner lock, so I wanted to make sure) and the lock bar didn't move a fraction of an inch. I can barely deform the handle at all. It is definitely very stiff, whether it is much stiffer than G-10 I can not say from personal experience, but many people say so. There is very little difference between the amount that I can bend the scales of a Manix and the CF Mili by pushing on the sides. Both move a little bit, but not much.
Again, IMHO and in the uses I put my knives through, the BG-42 turned out to be the best edge holder I have used so far. Of course I don't thin my blades out below about 12 deg. per side, so sofar I have not seen any problems with S30V (actually just crash the edge of my Manix with substantial force into some rebar, accidentally of course, which positively flattened a portion of the edge, but I didn't see any behavior that I wouldn't have expected such as undue chipping) so I would have ranked S30V or ZDP-189 as best edge holder before I got the CF Mili.
More pocketable......mmmh, I don't know about that. The Mili is lighter, slightly slimmer and not as wide, but it is quite a bit longer in the handle.
Bottom line is, that regardless of performance and certain annoying quirks (such as righhand tip down only and the plastic backspacer) it has truely captured my heart.