> IIUC, the goal of SpaceX's "Agile" approach to lower the costs of putting payloads into orbit via launch vehicle reuse by amortizing the R&D and equipment cost over multiple profitable launches.
An issue that's deeply intertwined with reusability is reliability. We put absolute emphasis on reliability with expendable launchers. But if you think about it, this is even more paramount in the case of reusable launchers. Hardware tends to degrade overtime, increasing the chance of triggering any design or manufacturing flaws. Expendable launchers need to contend with this only once and for a short time. Reusable launchers have to deal with it over several flights, several structural and thermal cycles (causing fatigue cracks) and a large accumulated operating time. Periodic maintenance can eliminate some flaws - but not design flaws. Launchers also tend to be very sensitive to design flaws, due to the very low engineering margins available. So, there is a bigger incentive here to get it right in the first try itself. (For example, consider the fact there are fewer entities with the capability to build the common turbofan engine than to build a rocket engine.)
Another point is that the agile methodology banks on one particular behavior of software. They rarely degrade over time (unless you manage to leak resources wildly). This makes it amenable to rapid trials, failures and corrections. The cost of experimentation is also minimal, since you don't lose hardware in the process. But in hardware projects, many flaws show up only after an extended period of testing. The trials and corrections are also costly and strenuous.
> They are searching for the cheapest route to achieve their goals.
You may have realized by now what I'm trying to convey. I'm not sure if the agile method is the cheapest route in space tech.
