The human form cylons are anatomically identical to humans. Only by looking for certain chemical compounds not present in humans, but present in limited amounts in the cylons can they be differentiated. There is no hard drive in there and the biological cyclons appear to have been developed by their mechanical counterparts. Even the mechanical ones appear more cybernetic than mechanical. It seems the early cyclons perfected biological computing and the Colonials can't even make sense out of it. As to intelligence, there really isn't any to be had from a cylon. They are master manipulators, even under the most adverse circumstances, and will manipulate the interrogators like a puppeteer. The problems with them mind-f**king you are greater than any intelligence they have to offer. It also shows that Laura Rosilyn (sp?) is not someone to mess with. She saw how phsychologically damaging having them around can be. The pregnant Boomer seems to be the only one that has developed her own free will and has abandoned the cyclons for the sake of her child. This could, of course, be nothing but a long term ruse.
I guess you're right; certainly the script seems to work that way. But there are a lot of silly things - why do Cylons glow when they have sex? That's something you ought be able to find. How do they upload and download? There should be a wireless system in there (whoo-hooo! A direct link to the OS!) that you can find and play with.
Also, they seem to be stronger than humans of the same mass - their muscle tissue should be different. Apparently they don't have the same need to eat or drink we do (although the Leobon seemed to enjoy his meal... which Starbuck thought was wretched) - they must have an internal power plant. Looks to me like there are a lot of basic, internal differences that would ID 'em.