I think many (though by no means all) restrictions on the use of money for campaign speech violate the First Amendment. I'm one of the few people who thinks Buckley v. Valeo is basically right, and contributions can generally be capped but expenditures (including corporate expenditures, a matter on which I disagree with the Court's Austin v. Michigan Chamber of Commerce precedent) cannot be. This means I'm not as critical of Sen. McCain's views as some of my conservative and libertarian friends are, but I certainly find much to disagree with in his views.
Still, let's be realistic: On the Court today, the liberal Justices are the ones who are most likely to uphold a wide range of campaign finance speech restrictions; Stevens, Ginsburg, and Breyer have even suggested that they would uphold limits on independent expenditures, which in my view would violate the core of the First Amendment. And the conservative Justices, including the moderate conservative Kennedy, are the ones who are most likely to strike down a wide range of such restrictions.
Perhaps McCain will appoint Justices who will end up being more likely to uphold such restrictions. But I'm pretty sure that he won't be a single-issue appointer on this matter. He's likely to appoint noted figures from the conservative legal movement, who are culturally and ideologically predisposed to be at least mildly skeptical of such restrictions, and likely to be (at worst) in the middle on this issue -- where O'Connor and Rehnquist mostly were -- and more likely where Kennedy, Alito, Roberts, and perhaps even Scalia and Thomas are.
On the other hand, I suspect that either Clinton or Obama would likely appoint noted figures from the liberal legal movement, who are culturally and ideologically predisposed to be open to such restrictions, and be where Stevens, Ginsburg, and Breyer are, or (at best) in the middle of this issue, where Souter has generally been. So my hesitation about many campaign finance speech restrictions is a reason to support McCain (despite my disagreement with him) rather than to oppose him. He's surely not perfect in my book, certainly not on this issue. But I think he'll be better than the alternatives, and to me elections -- especially general elections -- are all about the best option, not the perfect one.