[Pure Neutronium (OP)]

Of exploring and colonizing the solar system.  All other current or proposed propulsion systems are simply incapable of the speed or cargo capacity needed. 

[LeeE]

With reasonable economy and within a reasonable time-frame, probably yes.  With the STS (Shuttle) you're bringing a lot back down each time you send it up, which means that of the total amount of energy used to get the STS and its payload up into orbit, relatively less of it is spent on lofting the payload and relatively more on just lofting the launch vehicle, which then has to come back down again.

With simpler disposable rockets, you don't have the overhead of ensuring that the disposable parts are capable of surviving re-entry and being recoverable, or if they are, the equipment needed to survive re-entry and recovery can be simpler, meaning that they can be less heavily engineered and lighter, which means that for any given amount of launch energy, more of it is available for payload rather than launch vehicle.