Beyond Niccolo's points, there are questions here even for a reformer. Suppose Barr does get into the debates, something no previous LP candidate has done. Would this be good or bad? Well, there are people who don't know what libertarianism is - what conclusion will they draw when Barr speaks about DOMA, advocates sanctions, encourages the use of foreign aid for fighting drugs in South America, mentions his past with the CIA... This is beyond the conclusions they will draw just from seeing him there - such as that libertarians agreed with the Clinton impeachment and are a-ok with his get tough on crime mentality. So, right off the bat no leftist will be able to think about libertarianism without picturing Barr, an effect that poor candidates in the past didn't have, simply because they weren't well-exposed.
Also, libertarians, such as yourself, will be deluded into supporting him, as the LP candidate. I just read an LRC article where Dr. Block said that, as a libertarian, he is committed to supporting the LP candidate - how many think that way? Now, in Dr. Block's case, this won't result in him embracing Barr's non-libertarian stances, but not everyone thinks as clearly. If someone has libertarian instincts, but wants to be well-accepted in "polite society" they will have the excuse they need to embrace warfare.
Now, Niccolo does have a point that the Barr fiasco is an expected result of the Paul candidacy. First, it encouraged libertarians to work within politics, and accustomed them to mixing in conservatism with their libertarianism. It moved libertarians a step to the right, which opened them up to the next step - Barr. Next, it brought lots of conservatives, including far-right JBS types, into libertarianism, laying the groundwork for the paleocon takeover we're looking at if Barr is nominated.
Niccolo has made me think carefully about whether or not Paul was worth it. I think he was, but that this argument does give me reason to think. At the same time, I don't necessarily accept Niccolo's suggestion that this is an inevitable consequence - I think even if we say that the Paul campaign led to this, it remains a possibility that we could have had the Paul campaign without this. In fact, I think we can still fight it. That's why I wrote my LRC article on Barr the other day. It's also why LP radicals are building sites like badbarr2008.com , which the OP might care to look at. I am advocating that Ruwart be nominated, but I understand the heavy temptation Barr presents even to real libertarians - "wow, a candidate people have heard of! Who was a Congressman!" That's why I have suggested that the hardcore present Gravel as a fallback plan, a compromise. He is more of a classical liberal than Barr is, has as much if not more name recognition, was an elected Senator, and will not alienate the left. He's better than Barr, I propose.