The Augustine report describes the Flexible Path as an incrementally more ambitious and difficult series of deep space missions. The wording of the Flexible Path description seems to indicate that, while exploration capabilities increase gradually on this path, there is little infrastructure built up from mission to mission, and little long-term use of the various deep space destinations. In a sense the deep space missions could be considered "one-offs" that eventually allow us to reach the surface of Mars. For example, the report says
In every flight, the Flexible Path voyages would visit places where humans have never been before, with each mission extending farther than the previous one ...
Clearly, if each mission extends farther than the previous one, we are not lingering at the various destinations.
The report describes several missions to near-Earth objects, but each near-Earth object is a unique destination. The other destinations don't seem to imply or require repeated visits. It is suggested that the Earth-Moon L1 point destination might involve a fuel depot, but no other space infrastructure is implied in the Flexible Path.
I would suggest that the Flexible Path be modified to potentially revisit earlier destinations as appropriate for
- building space infrastructure such as small habitats or stations, depots, servicing nodes, and assembly areas to enable exploration and resource use
- additional science benefits such as improved data gathering following analysis of data from earlier Flexible Path missions
- incremental improvement of engineering and science capabilities at each destination, such as additional observatory servicing capabilities, additional telerobotics missions, and improved science instruments
- making later exploration steps safer, easier, and more productive through carefully repeated testing of exploration systems at each Flexible Path step and build-up of exploration-enabling space infrastructure
- more thorough extraction of resources at NEOs if the early NEO ISRU demos show promise
- enabling commerce and purchasing commercial services at the various destinations
In a limited budget, the adjustment I've described would come at a price. Our journey along the Flexible Path would be slower. That's not a trivial price. However, a slower journey is probably justified if it results in getting more benefits out of each step.