Yes DavidBrown; the pygmy marmoset exhibit was built to show comparison between the largest and smallest primate. I agree that it doesn't 100% fit and I have rarely ever seen them on exhibit.
As for the Goliath beetles, yes they were on exhibit in Congo. Between Jungle World and Congo the Bronx Zoo has several different beetle species.
I'd rather see talapoin, pangolin, or some other small West African species in the enclosure, especially since it's empty 90% of the time. Hell, I'd even take the giant elephant-shrews since they're at least African.
~Thylo