Dr. Monygham's prophetic remark deliberately echoes the chief engineer's comment about "spiritual value" above. Since the People act only in their own interest, they must receive some illusory value (such as prestige) for remaining loyal to the cause of material interests, for they certainly don't receive any material value. In the remainder of the paragraph, Monygham contrasts Nostromo to Gamacho, who has received plenty of material reward precisely because he could never have achieved Nostromo's kind of prestige.