It's made clear they are devoid of emotion, but is it a stretch to consider they are devoid of imagination? Of inspiration?
If so....how long could our world last without any new inventions, any progress?
I imagine it would only be a matter if time before the pods grew tired of our planet and moved on to another, much like they did during the credit sequence of this version.
"If so....how long could our world last without any new inventions, any progress?"
In Jack Finney's original novel it was said the pod duplicates only last for five years. As more and more people were being replaced by duplicates, the narrator described how shabby and untidy the town was looking.
After every human had been taken over in the film, I was guessing that progress would have come to a standstill. Assuming the pods were still living on Earth in 2015, it would probably still look like 1978. As Geoffrey said to Elizabeth, "Nothing changes, you can have the same house, same clothes, same car." All the pods can do is imitate. They can absorb knowledge, but they can't absorb imagination, creativity or fashion sense.
Even if there aren't any humans left to duplicate, the pods can work their way down through the rest of the flora and fauna. So they could potentially be on Earth for billions of years, until the sun becomes a red giant and the planet is dying - forcing the pods to move on yet again.
The pod people were NOT completely emotionless, they were supposed to be since they were just a life form performing a biological imperative to reproduce but I believe any sentient being has SOME emotion even if only a tiny amount. I call it "micro emotion" and I have seen it in other fictional characters that are supposed to be emotionless. In Star Trek Next Gen Data obviously cared about his friends more than a totally emotionless being could have even before he got his emotion chip and in Terminator 2 Judgement Day Arnold even said "I now understand why humans cry even though it is something I could never do".
An example of a tiny amount of emotion was a tiny bit of COMPASSION. Leonard Nimoy (Kibner) and Jeff Goldblum both tried to comfort a terrified Donald Southerland and Brooke Adams to make them less afraid. It failed horribly of course but they did try. Instead of just knocking them out they were given a mild sedative. In the original book the main hero Miles to buy time asked if he and his love could at least be alone in a room together with a little privacy and the request was granted. I think the pods had a very tiny amount of emotion that is mandatory for any sentient being but it was very tiny, but they were not completely emotionless like a computer or lower life form.
I also noticed a little bit of anger, when Donald destroyed their green house and one of them said "We'll get him, he can't stay awake forever" he seemed a tad angry. In the original novel when Miles was stalling for time engaging pod people who were holding them prisoner in conversation one of the pod people said the swear word "hell" in a monotone at one point when admitting that they would only live for five years, something he was not happy about I guess, and the narrator said "that was the closest to anger they were capable of coming".