Liquids do not need more launches, quite the opposite. The highest-capacity Atlas V variants are completely liquid fueled. It'd take six Liberty launches to equal one Saturn V launch. The Liberty first stage is big enough that there have been major problems with actually implementing it, in spite of deriving from an existing, only slightly smaller system, while the competing all-liquid systems have plenty of room for growth and have proven far more flexible overall. Contrast the expense and difficulty of reworking Shuttle SRBs to the reuse of engines between Falcon 1 and Falcon 9, the extended tanks of the v1.1 Falcon 9, the concepts for future upgrades with a Merlin 2 engine, etc. If solids aren't even a part of manned LEO launches, there's no reason to think they'll have anything to do with Mars.