Space Station was cancelled, restarted, delayed, changed, funding cut, etc. in the 1980s, 1990s, 2000s and so on. There NEVER was a "clear vision" for WHY we neede ISS other than a place for the Shuttle to go. I worked on at least two iterations of "ISS". The moon mission was a side effect of the Cold War and somewhat a legacy of JFK. There was some really cool inventions that came out of the program and were commercialized and lots of technology invented that went on to be used for many years.
Right now, the leaders in invention and technology for Space is in the commercial sector, but there is not a heavy lift MAN-RATED launch platform in the US commerical or NASA inventory at this time. There were some other alternatives that were proposed that were strictly heavy lift for manned missions but they were shot down for the Aries that was more "scalable" for many types of missions. This was a mistake as those other missions are being filled right now by commerical ventures like Atlas and Titan IV. Maybe it was a case of NASA wanted the whole launch "business" to itself like back in the 1960s. If the program was refocused on building a simple, efffective man-rated heavy lift launch vehicle (think Saturn V but modern) I think something could be ready in a few years. Granted we might have to "license" some engine technology from the Russians but it is doable. Spending more $$$ on R&D isn't going to progress anything. A TON of research was done in the 1960s and 1970s that can be reused, updated and put into practice, there really isn't a lot of NEW things the R&D money is going to invent. Just a different kind of "pork".