I highly doubt much if any of the space exploration now is going to have a significant impact on humans being an interplanetary or interstellar species. A good analog might be the heroic age of Antarctic exploration. It was interesting, but it Amundsen's expedition never left we'd be in the exact same place we are now when it comes to exploring Antarctica.
If 200 years ago a country had decided to keep a settlement going at the top of Mount Everest in the name of progress, it wouldn't have been any benefit to the modern efforts to keep people in the ISS. Likewise, I don't expect the ISS to have any noticeable impact on efforts to have people live on other planets.
Keep in mind, this doesn't mean we won't make progress. A lot of people are excited about what SpaceX has been doing, and until very recently they've been entirely involved in non-human cargo. There are a lot of reasons to send things into space, which is why we send up a lot of stuff. There's just not many reasons to send people up at the moment, other than to be able to say we're sending people up.
We have to start somewhere, and private industry isn't going to start it because, as you point out, there's not many reasons to do it at the moment. The ISS is allowing us to experiment with living in orbit for extended periods. We certainly have to master those relatively simple conditions before attempting to survive a manned trip to Mars or living on the Moon.
Also SpaceX wouldn't exist without the ISS. It's NASA contracts for resupplying the ISS that kept it alive in the early days. Which just goes to prove the model: Government invests in "useless" project that allows private industry the toe-hold of capital needed to kickstart a new technology.
To your Antarctic exploration analogy, I'd say the ISS is more equivalent to McMurdo station than the Amundsen expedition
If 200 years ago a country had decided to keep a settlement going at the top of Mount Everest in the name of progress, it wouldn't have been any benefit to the modern efforts to keep people in the ISS. Likewise, I don't expect the ISS to have any noticeable impact on efforts to have people live on other planets.
Keep in mind, this doesn't mean we won't make progress. A lot of people are excited about what SpaceX has been doing, and until very recently they've been entirely involved in non-human cargo. There are a lot of reasons to send things into space, which is why we send up a lot of stuff. There's just not many reasons to send people up at the moment, other than to be able to say we're sending people up.