Jim Henley at Unqualified Offerings with some thoughts on why Rand Paul won't get away with being Ron Paul, even were he so inclined (while riffing off Daniel Larison's defense in The Week of Rand's anti-military bonafides):
If [Rand Paul] does get elected, it'll be interesting to see what his antiwar and antsurveillance-state inclinations amount to in practice. Paul the Greater has been able to flout the contempt of the Republican establishment for several reasons, including providing great constituent-service (from what I've read), and blanketing his district with a whole lot of campaign spending come reelection time. Both are harder for a Senator to pull off.
Beyond that, though, I think Ron Paul benefits from being, when all is said and done, inconsequentiual….in terms of getting Congress to put any of his ideas into law. It's to Paul's credit that he opposed the Iraq War and the Patriot Act, but his opposition didn't stop anything.
But the Senate is smaller, so a single Senator matters a lot. That means that if Rand Paul bucks the GOP leadership on a core principle – e.g. "All War, All the Time"; "Ever More Surveilance Every Moment" – there's a chance it could actually matter. (We're assuming Paul wants to try.) A dissident Congressman is a colorful sideshow. A dissident Senator is a damned inconvenience. So if the Republican Party of 2016 is the same, lovable "I know he's an American citizen, but still" Republican Party of 2010, and Little Paul makes any serious trouble on its core issues of dominating foreigners and shoveling money to Erik Prince and General Dynamics, the Republican leadership will land on his primary season like a MOAB.