That was Ryan O'Neal opposite Streisand in "What's Up Doc" and I also always wished Babs would stick to singing -- not that much of a fan of her acting. But she is a good comedian, probably from her experience in "Funny Girl" portraying Fanny Brice and O'Neal was a good foil for her in that film. It was Bognavich's directing that made the film, however. Madelaine Kahn virtually ran away with the show as the jilted fiancee.
It's really a remake of "Bringing Up Baby" cleverly disguised but the spy storyline with the mixed up bags is hilarious. You're right that Streisand is no Katherine Hepburn and Ryan O'Neal is no Cary Grant but still a

comedy.
"Bringing Up Baby" has to be up there in the top ten -- that final scene when she's made a mess of Cary Grant's life and destroys the dinosaur specimen is uproarious. And who could forget the "gay" line when Cary Grant is caught wearing the woman's housecoat.