The MPAA and RIAA would be less powerful under a Ron Paul presidency, because most of their power right now is thanks to lobbying Congress for special treatment. They frequently get extensions of copyright terms and they have government agencies like the FBI doing anti-piracy work. This is a huge subsidy for them. My guess is that Ron Paul would veto any bills that give them special treatment and would probably direct government agencies to shift their priorities.
IMO, the MPAA and RIAA should have to sue in civil court if they think someone is guilty of piracy, instead of having taxpayer-funded preemptive enforcement. Let them do their own dirty work. I don't know if Ron Paul agrees with this or not, though.