The ISS, IMHO, should be a base station for further exploration. We should have one set of craft for getting people from earth to the ISS and set to go from the ISS to the various "targets". I think one of the barriers we've had is that while the shuttle is great for earth to orbit and back (inspite of the weekend's events let's keep in mind that it really does have a good track record, not great but good) that's about all it's good for, can't land on rough terrain, can't take off without the booster. Meanwhile the old style landers are no good for earth to orbit. Instead of seeing this as weakness it should be the source of the plan.
The original plan was quite a bit bigger than what we ended up with. There was the Space Shuttle, a cheap way to get to orbit and back. There was the Space Station, something a lot more capable and bigger than the ISS. There were other craft, some capable of going to the moon and back like an express shuttle, a moon base, and perhaps a station orbiting the moon. We built only the first part of the system. The system could be expanded to include regular service to and from Mars the same way.
There were several alternative designs for the system, but it wasn't ever intended to go just between earth surface and LEO.
The complete system was a good idea, lots of redundancy, pretty good safety, and excellent efficiency in the cost area compared to the one-off missions we have conducted ever since Apollo.