You are right about the fact that many audience members might already be in the choir. However, there are also some other benefits with this action...
...This action supports Noory and Coast to Coast in a financial way. We will see the 9/11 Truth message repeated by Coast to Coast and George Noory during other broadcast conversations and interludes. In effect, this becomes 'free advertising' because of the air time.
...some listeners might have glimpsed at the first Loose Change film years ago and made the decision at that time in support of the government's story. These listeners have it "justified" that they have already researched the subject by glimpsing at the first Loose Change movie. With this national advertising action, it puts a renewed focus onto 9/11 Truth and also a huge emphasis from a scientific and engineering perspective. In other words, these listeners might give it a "second look".
...This elevates the topic to a higher credibility in the mind of the public, because it is advertised. The public tends to give more altitude towards those things which are advertised.
...This action repeatedly puts people's attention on the subject.
...Many people already know about 9/11 Truth. However, they might have dropped to the wayside over the years. This advertising might rehabilitate their vigor of support for the subject.
...As 9/11 Truth receives more and more media exposure, we will also see more and more people support AE911Truth.org in a financial way. The esprit and excitement of media exposure helps in recruiting funds.
(There have been many people who have quietly contributed money to the cause. My hat is off to them. Thankyou.)

On reaching new public... ...new public are optimally reached "on the first time out with a medium". This is when the message gets the cream of new exposures. Over time, fewer and fewer audience members of that medium will be "new public". truthoverprofit, I think that this is your concern. However, this is the first NATIONAL ad campaign, so we will likely pick up new ears.

My guesstimation would be that MAYBE 2%, at the very most, of the C2C audience are pro-9/11 Truth.
And probably not even that many. Probably more like 1/2 of 1%, if even that. (it's difficult for me to even
be as realistic as I probably should in guesstimating the numbers, because it's a little upsetting and irritating)

It's very obvious that the 9/11 Truth Movement isn't anywhere near as big as some people claim.
I doubt if it's even 50,000 strong. (actual, semi-active, and fairly supportive and knowledgeable people)

Otherwise things would be much different than they are today.

All you have to do is do some tabling and that sort of thing, and you will find that probably,
easily less than 5 in 100 are minimally knowledgeable about 9/11 Truth and its issues,
and less than that truly support it. (AT LEAST 70% of the general population STILL do not know about
WTC 7, and I'm probably being overly generous in that estimation)

At this late date it's a sad fact and unfortunate state of affairs.

And there is a lot of other anecdotal evidence, as well.

AFAIK, and last I heard, there aren't even 'official' 9/11 Truth student groups at UC San Franciso, UC Davis,
UC Chico, and Sac State, here in California. (or at most of the other state colleges and universities, or
the two-year and community colleges) And I've heard it's basically the same across the U.S.

Most cities still do not have actual groups, and those few that do (relatively speaking), are seriously low
in numbers for their 'membership' and supportership based on per capita population numbers.

This is also evidenced by the attendance of conventions and seminars and AE911Truth presentations,
where they struggle to fill small events, although it is somewhat better now than last year, etc. as one
would expect. But, even if you get 250 people at an event in a city with a population of several tens of thousands,
or more, the numbers speak for themselves.

One recent AE911Truth example is the San Leandro event, which had 250 in attendance (most of whom were probably
under the category of preaching to the choir), which is a pretty good turn out, because they usually and traditionally
are not that high, with a population of about 83,000 (although technically it's actually larger than that because in the
Bay Area, all of the cities are right up next to each other), they got about 1/3 of 1%.

So that is a pretty realistic number. (and I think probably, generally, nationwide a little, or a lot, high)

The adult (over 18) population in the U.S. is about 200 million, or so. 1% of that is 2 million, and 1/3 of that is
about 666 thousand. (OMG! that number can't be a coincidence!!!! ;o) ) I suppose there could be 666K 9/11 Truth
"supporters" in the U.S., but I highly doubt it. (that averages to ~ 13K per state, which is probably high)

So we need to not shy away from the reality of the situation, because that does no one any good.